Re-dispersed microfibrillated cellulose

ABSTRACT

Methods of improving the re-dispersibility of dried or at least partially dried microfibrillated cellulose, methods of re-dispersing dried or at least partially dried microfibrillated cellulose, compositions comprising re-dispersed microfibrillated cellulose and the use of re-dispersed microfibrillated cellulose in an article, product or composition; and methods of improving the physical and/or mechanical properties of re-dispersed dried or partially dried microfibrillated cellulose.

TECHNICAL FIELD

The present invention relates generally to methods of improving there-dispersibility of dried or at least partially dried microfibrillatedcellulose and methods of re-dispersing dried or at least partially driedmicrofibrillated cellulose. The methods may, for example, comprisedewatering the aqueous composition, optionally followed by drying. There-dispersing microfibrillated cellulose may, for example, comprisere-dispersing dried or at least partially dried microfibrillatedcellulose in a liquid medium and in the presence of an additive otherthan inorganic particulate material and/or in the presence of acombination of inorganic particulate materials. The additive and/orcombination of inorganic particulate materials may, for example, enhancea mechanical and/or physical property of the re-dispersedmicrofibrillated cellulose. The present invention further relates tocompositions comprising re-dispersed microfibrillated cellulose and theuse of re-dispersed microfibrillated cellulose in an article, product orcomposition.

BACKGROUND OF THE INVENTION

In recent years microfibrillated cellulose and compositions comprisingsame has been shown to have a variety of useful properties, includingthe enhancement of the mechanical, physical and/or optical properties ofa variety of products, such as paper, paperboard, polymeric articles,paints, and the like. Typically prepared in aqueous form, it is normallydried for transport in order to reduce its weight and associatedtransportation costs. The end-user will then typically re-disperse themicrofibrillated cellulose prior to use in the intend end-use. However,following drying and re-dispersion some or all of its advantageousproperties are diminished or lost. Thus, there is an ongoing need toimprove the properties of microfibrillated cellulose following dryingand re-dispersal.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention there isprovided a method of improving the re-dispersibility of dried or atleast partially dried microfibrillated cellulose, comprising drying orat least partially drying an aqueous composition of microfibrillatedcellulose by a method comprising:

-   -   (i) dewatering the aqueous composition by one or more of:        -   (a) dewatering by belt press, for example, high pressure            automated belt press, (b) dewatering by centrifuge, (c)            dewatering by tube press, (d) dewatering by screw press,            and (e) dewatering by rotary press; followed by drying,    -   or    -   (ii) dewatering the aqueous composition, followed by drying by        one or more of:        -   (f) drying in a fluidized bed dryer, (g) drying by microwave            and/or radio frequency dryer, (h) drying in a hot air swept            mill or dryer, for example, a cell mill or an atritor mill,            and (i) drying by freeze drying;    -   or    -   (iii) any combination of dewatering according to (i) and drying        according to (ii),    -   or    -   (iv) a combination of dewatering and drying the aqueous        composition,    -   where upon re-dispersing the dried or at least partially dried        microfibrillated cellulose in a liquid medium, the re-dispersed        microfibrillated cellulose has a mechanical and/or physical        property which is closer to that of the microfibrillated        cellulose prior to drying or at least partial drying than it        would have been but for drying according to (i), (ii), (iii) or        (iv), optionally wherein the dried or at least partially dried        microfibrillated cellulose comprises inorganic particulate        material and/or an additive, the presence of which enhances a        mechanical and/or physical property of the re-dispersed        microfibrillated cellulose.

In certain embodiments, the method further comprises re-dispersing thedried or at least partially dried microfibrillated cellulose in theliquid medium, and optionally further comprising using the re-dispersedmicrofibrillated cellulose in the manufacture of an article, product orcomposition.

In accordance with a second aspect of the present invention there isprovided a method of re-dispersing microfibrillated cellulose, themethod comprising re-dispersing dried or at least partially driedmicrofibrillated cellulose in a liquid medium, wherein the dried or atleast partially dried microfibrillated cellulose was prepared bydewatering and drying an aqueous composition comprising microfibrillatedcellulose whereby the re-dispersed microfibrillated cellulose has amechanical and/or physical property which is closer to that of themicrofibrillated cellulose prior to drying or at least partial dryingthan it would have been but for said dewatering and drying, optionallywherein the dried or at least partially dried microfibrillated cellulosecomprises: (i) inorganic particulate material, (ii) a combination ofinorganic particulate materials, and/or (iii) an additive other thaninorganic particulate material, the presence of which duringre-dispersing enhances a mechanical and/or physical property of there-dispersed microfibrillated cellulose; and wherein dewatering isselected from one or more of:

-   -   (a) dewatering by belt press, for example, high pressure        automated belt press;    -   (b) dewatering by centrifuge;    -   (c) dewatering by tube press;    -   (d) dewatering by screw press; and    -   (e) dewatering by rotary press;    -   and/or wherein drying is selected from one or more of:    -   (f) drying in a fluidized bed dryer;    -   (g) drying by microwave and/or radio frequency dryer    -   (h) drying in a hot air swept mill or dryer, for example, a cell        mill or an atritor mill; and    -   (i) drying by freeze drying.

In accordance with a third aspect of the present invention there isprovided a method of improving the physical and/or mechanical propertiesof re-dispersed dried or partially dried microfibrillated cellulose, themethod comprising:

-   -   a. providing: an aqueous composition of microfibrillated        cellulose;    -   b. dewatering the aqueous composition by one or more of: (i)        dewatering by belt press, (ii) a high pressure automated belt        press, (iii) centrifuge, (iv) tube press, (v) screw press,        and (vi) rotary press;

to produce a dewatered microfibrillated cellulose composition;

-   -   c. drying the dewatered microfibrillated cellulose composition        by one or more of: (i) a fluidized bed dryer, (ii) microwave        and/or radio frequency dryer, (iii) a hot air swept mill or        dryer, a cell mill or a multirotor cell mill, and (iv) freeze        drying;

to produce a dried or partially dried microfibrillated cellulosecomposition;

whereupon re-dispering the dried or partially dried microfibrillatedcellulose composition into a liquid medium, the microfibrillatedcellulose has a tensile index and/or viscosity which is at least 50% ofthe tensile index and/or viscosity of the aqueous composition ofmicrofibrillated cellulose prior to drying at a comparable concentrationand a fibre steepness of from 20 to 50.

In accordance with a forth aspect of the present invention there isprovided a method of re-dispersing microfibrillated cellulose, themethod comprising re-dispersing dried or at least partially driedmicrofibrillated cellulose in a liquid medium and in the presence of anadditive other than inorganic particulate material which enhances amechanical and/or physical property of the re-dispersed microfibrillatedcellulose, wherein the microfibrillated cellulose prior to being driedor at least partially dried has a fibre steeness of from 20 to 50.

In accordance with a fifth aspect of the present invention there isprovided a method of re-dispersing microfibrillated cellulose, themethod comprising re-dispersing dried or at least partially driedmicrofibrillated cellulose in a liquid medium and in the presence of acombination of inorganic particulate materials, wherein the combinationof inorganic particulate materials enhances a mechanical and/or physicalproperty of the re-dispersed microfibrillated cellulose, optionallywherein the combination of inorganic particulate materials comprisescalcium carbonate and a platy mineral.

In accordance with a sixth aspect of the present invention there isprovided a composition comprising re-dispersed microfibrillatedcellulose dispersed in a liquid medium and which is obtainable/obtainedby a method according to any aspect or embodiment of the presentinvention, and having, at a comparable concentration, a tensile indexand/or viscosity which is at least 50% of the tensile index and/orviscosity of the aqueous composition of microfibrillated cellulose priorto drying, wherein either (i) the microfibrillated cellulose of theaqueous composition has a fibre steepness of from 20 to 50, and/or (ii)the aqueous composition of microfibrillated cellulose comprisesinorganic particulate material.

In accordance with a seventh aspect of the present invention there isprovided use of re-dispersed microfibrillated cellulose according to anyaspect or embodiment of the present invention. In certain embodiments,the microfibrillated cellulose is used in an article, product orcomposition. Thus, in accordance with a further aspect of the presentinvention there is provided an article, product or compositioncomprising a microfibrillated cellulose according to any aspect orembodiment of the present invention.

The details, examples and preferences provided in relation to anyparticular one or more of the stated aspects of the present inventionapply equally to all aspects of the present invention. Any combinationof the embodiments, examples and preferences described herein in allpossible variations thereof is encompassed by the present inventionunless otherwise indicated herein, or otherwise clearly contradicted bycontext.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a summary of the effect of the use of a single disc refineron dried composition comprising microfibrillated cellulose and calciumcarbonate materials.

DETAILED DESCRIPTION OF THE INVENTION

Seeking to improve one or more properties of re-dispersedmicrofibrillated cellulose and compositions comprising same, it hassurprisingly been found that a combination of dewatering and drying, forexample, mechanical dewatering and drying, an (never before dried)aqueous composition comprising microfibrillated cellulose, optionally inthe presence of an inorganic particulate and/or other additive as hereindescribed, can be implemented in order to enhance or improve one or moreproperties of the microfibrillated cellulose upon re-dispersal. That isto say, compared to the microfibrillated cellulose prior to drying, theone or more properties of the re-dispersed microfibrillated are closerto the one or properties of the microfibrillated cellulose prior todrying than it/they would have been but for the combination ofdewatering and drying. Similarly, it has surprisingly been found thatthe incorporation of inorganic particulate material, or a combination ofinorganic particulate materials, and/or other additives as hereindescribed, can enhance the re-dispersibility of the microfibrillatedcellulose following initial drying.

Thus, in certain embodiments, the method of improving there-dispersibility of dried or at least partially dried microfibrillatedcellulose comprises drying or at least partially drying an aqueouscomposition by a method comprising:

-   -   (i) dewatering the aqueous composition by one or more of:        -   (a) dewatering by belt press, for example, high pressure            automated belt press, (b) dewatering by centrifuge, (c)            dewatering by tube press, (d) dewatering by screw press,            and (e) dewatering by rotary press; followed by drying,    -   or    -   (ii) dewatering the aqueous composition, followed by drying by        one or more of:        -   (f) drying in a fluidized bed dryer, (g) drying by microwave            and/or radio frequency dryer, (h) drying in a hot air swept            mill or dryer, for example, a cell mill or an atritor mill,            and (i) drying by freeze drying;    -   or    -   (iii) any combination of dewatering according to (i) and drying        according to (ii), or    -   (iv) a combination of dewatering and drying the aqueous        composition.

In certain embodiments, if drying is by freeze drying, dewateringcomprises one or more of (a) to (e).

Upon subsequent re-dispersal, e.g., following transportation to anotherfacility, of the dried or at least partially dried microfibrillatedcellulose in a liquid medium, the re-dispersed microfibrillatedcellulose has a mechanical and/or physical property which is closer tothat of the microfibrillated cellulose prior to drying or at leastpartial drying than it would have been but for drying according to (i),(ii), (iii) or (iv).

Thus, in accordance with another aspect, there is provided a method ofre-dispersing microfibrillated cellulose, the method comprisingre-dispersing dried or at least partially dried microfibrillatedcellulose in a liquid medium, wherein the dried or at least partiallydried microfibrillated cellulose was prepared by dewatering and dryingan aqueous composition comprising microfibrillated cellulose whereby there-dispersed microfibrillated cellulose has a mechanical and/or physicalproperty which is closer to that of the microfibrillated cellulose priorto drying or at least partial drying than it would have been but forsaid dewatering and drying, optionally wherein the dried or at leastpartially dried microfibrillated cellulose comprises: (i) inorganicparticulate material, (ii) a combination of inorganic particulatematerials, and/or (iii) an additive other than inorganic particulatematerial, the presence of which during re-dispersing enhances amechanical and/or physical property of the re-dispersed microfibrillatedcellulose; and optionally wherein dewatering is selected from one ormore of:

-   -   (a) dewatering by belt press, for example, high pressure        automated belt press;    -   (b) dewatering by centrifuge;    -   (c) dewatering by tube press;    -   (d) dewatering by screw press; and    -   (e) dewatering by rotary press;

and/or wherein drying is selected from one or more of:

-   -   (f) drying in a fluidized bed dryer;    -   (g) drying by microwave and/or radio frequency dryer    -   (h) drying in a hot air swept mill or dryer, for example, a cell        mill or an atritor mill; and    -   (i) drying by freeze drying;

In certain embodiments, if drying was by freeze drying, dewateringcomprises one or more of (a) to (e).

Thus, in accordance with another aspect, there is provided a method ofimproving the physical and/or mechanical properties of re-disperseddried or partially dried microfibrillated cellulose, the methodcomprising:

-   -   a. providing: an aqueous composition of microfibrillated        cellulose;    -   b. dewatering the aqueous composition by one or more of: (i)        dewatering by belt press, (ii) a high pressure automated belt        press, (iii) centrifuge, (iv) tube press, (v) screw press,        and (vi) rotary press;

to produce a dewatered microfibrillated cellulose composition;

-   -   c. drying the dewatered microfibrillated cellulose composition        by one or more of: (i) a fluidized bed dryer, (ii) microwave        and/or radio frequency dryer, (iii) a hot air swept mill or        dryer, a cell mill or a multirotor cell mill, and (iv) freeze        drying;

to produce a dried or partially dried microfibrillated cellulosecomposition;

whereupon re-dispering the dried or partially dried microfibrillatedcellulose composition into a liquid medium, the microfibrillatedcellulose has a tensile index and/or viscosity which is at least 50% ofthe tensile index and/or viscosity of the aqueous composition ofmicrofibrillated cellulose prior to drying at a comparable concentrationand a fibre steepness of from 20 to 50.

The following sections pertain to any of the aspects described above.

References to “dried” or “drying” includes “at least partially dried” or“or at least partially drying”.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is dewatered by belt press, for example, highpressure automated belt press, followed by drying, for example, via oneor more of (f) to (i) above.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is dewatered by centrifuge, followed bydrying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is dewatered by tube press, followed bydrying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is dewatered by screw press, followed bydrying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is dewatered by rotary press, followed bydrying, for example, via one or more of (f) to (i) above.

In certain embodiments, the aqueous composition is dewatered, forexample, via one or more of (a) to (e) above, and then dried in afluidized bed dryer.

In certain embodiments, the aqueous composition is dewatered, forexample, via one or more of (a) to (e) above, and then dried bymicrowave and/or by radio frequency drying.

In certain embodiments, the aqueous composition is dewatered, forexample, via one or more of (a) to (e) above, and then dried in a hotair swept mill or dryer, for example, a cell mil or an Atritor mill. AnAtritor mill may be an Atritor dryer-pulveriser, an Attritor Cell Mill,an Atritor Extended classifier mill or an Atritor Air Swept Tubular(AST) dryer (Atritor Limited, 12 The Stampings, Blue Ribbon Park,Coventry, West Midlands, England). Such mills may be used to prepare theaqueous composition of microfibrillated cellulose which is subsequentlydried and then re-dispersed.

In certain embodiments, the aqueous composition is dewatered, forexample, via one or more of (a) to (e) above, and then dried by freezedrying. In certain embodiments, dewatering is by one or more of (a)-(e)described above.

Dewatering and drying may be carried out for any suitable period oftime, for example, from about 30 minutes to about 12 hours, or fromabout 30 minutes to about 8 hours, or from about 30 minutes to about 4hours, or from about 30 minutes to about 2 hours. The period of timewill be depend on factors such as for example, the solids content of theaqueous composition comprising microfibrillated cellulose, the bulkamount of the aqueous composition comprising microfibrillated celluloseand the temperature of drying.

In certain embodiments, drying is conducted at a temperature of fromabout 50° C. to about 120° C., for example, from about 60° C. to about100° C., or at least about 70° C., or at least about 75° C., or at leastabout 80° C.

In certain embodiments, the method further comprises re-dispersing thedried or at least partially dried microfibrillated cellulose in a liquidmedium, which may be aqueous or non-aqueous liquid. In certainembodiments, the liquid medium is an aqueous liquid, for example, water.In certain embodiments, the water is a waste water or a recycled wastewater derived from the manufacturing plant in which the re-dispersedmicrofibrillated cellulose is being used to manufacture an article,product or composition. For example, in paper/paper board manufacturingplants, the water may be or comprise recycled white water from the papermaking process. In certain embodiments, at least portion of anyinorganic particulate material and/or additive other than inorganicparticulate material be present in the recycle white water.

In certain embodiments, the method further comprises using there-dispersed microfibrillated cellulose in the manufacture of anarticle, product or composition, which are many and various and include,without limitation, paper and paperboard, polymeric articles, productsand compositions, and other compositions such as coatings, e.g., paint.

In certain embodiments the dried or at least partially driedmicrofibrillated cellulose comprises inorganic particulate materialand/or an additive, the presence of which enhances a mechanical and/orphysical property of the re-dispersed microfibrillated cellulose. Suchinorganic particulate materials and additives are described herein inbelow.

The aqueous composition comprising microfibrillated cellulose may bedewatered and dried in order to reduce water content by at least 10% byweight, based on the total weight of the aqueous composition comprisingmicrofibrillated cellulose prior to dewatering and drying, for example,by at least 20% by weight, or by at least 30% by weight, or by at least40% by weight, or by at least about 50% by weight, or by at least 60% byweight, or by at least 70% by weight, or by at least 80% by weight, orby at least 80% by weight, or by at least 90% by weight, or by at leastabout 95% by weight, or by at least about 99% by weight, or by at leastabout 99.5% by weight, or by at least 99.9% by weight.

By “dried” or “dry” is meant that the water content of the aqueouscomposition comprising microfibrillated cellulose is reduced by at least95% by weight.

By “partially dried” or “partially dry” is meant that the water contentof the aqueous composition comprising microfibrillated cellulose isreduced by an amount less than 95% by weight. In certain embodiments,“partially dried” or “partially dry” means that the water content of theaqueous composition comprising microfibrillated cellulose is reduced byat least 50% by weight, for example, by at least 75% by weight, or by atleast 90% by weight.

The aqueous composition comprises microfibrillated cellulose. By“microfibrillated cellulose” is meant a cellulose composition in whichmicrofibrils of cellulose are liberated or partially liberated asindividual species or as smaller aggregates as compared to the fibres ofa pre-microfibrillated cellulose. The microfibrillated cellulose may beobtained by microfibrillating cellulose, including but not limited tothe processes described herein. Typical cellulose fibres (i.e.,pre-microfibrillated pulp) suitable for use include larger aggregates ofhundreds or thousands of individual cellulose microfibrils. Bymicrofibrillating the cellulose, particular characteristics andproperties, including but not limited to the characteristic andproperties described herein, are imparted to the microfibrillatedcellulose and the compositions including the microfibrillated cellulose.

The microfibrillated cellulose may be derived from any suitable source,as described herein.

Unless otherwise stated, particle size properties referred to herein forthe inorganic particulate materials are as measured in a well-knownmanner by sedimentation of the particulate material in a fully dispersedcondition in an aqueous medium using a Sedigraph 5100 machine assupplied by Micromeritics Instruments Corporation, Norcross, Ga., USA(telephone: +1 770 662 3620; web-site: www.micromeritics.com), referredto herein as a “Micromeritics Sedigraph 5100 unit”. Such a machineprovides measurements and a plot of the cumulative percentage by weightof particles having a size, referred to in the art as the ‘equivalentspherical diameter’ (e.s.d), less than given e.s.d values. The meanparticle size d₅₀ is the value determined in this way of the particlee.s.d at which there are 50% by weight of the particles which have anequivalent spherical diameter less than that d₅₀ value.

Alternatively, where stated, the particle size properties referred toherein for the inorganic particulate materials are as measured by thewell-known conventional method employed in the art of laser lightscattering, using a Malvern Mastersizer S machine as supplied by MalvernInstruments Ltd (or by other methods which give essentially the sameresult). In the laser light scattering technique, the size of particlesin powders, suspensions and emulsions may be measured using thediffraction of a laser beam, based on an application of Mie theory. Sucha machine provides measurements and a plot of the cumulative percentageby volume of particles having a size, referred to in the art as the‘equivalent spherical diameter’ (e.s.d), less than given e.s.d values.The mean particle size d₅₀ is the value determined in this way of theparticle e.s.d at which there are 50% by volume of the particles whichhave an equivalent spherical diameter less than that d₅₀ value.

Unless otherwise stated, particle size properties of themicrofibrillated cellulose materials are as measured by the well-knownconventional method employed in the art of laser light scattering, usinga Malvern Mastersizer S machine as supplied by Malvern Instruments Ltd(or by other methods which give essentially the same result).

In certain embodiments, the microfibrillated cellulose has a d₅₀ rangingfrom about 5 to μm about 500 μm, as measured by laser light scattering.In certain embodiments, the microfibrillated cellulose has a d₅₀ ofequal to or less than about 400 μm, for example equal to or less thanabout 300 μm, or equal to or less than about 200 μm, or equal to or lessthan about 150 μm, or equal to or less than about 125 μm, or equal to orless than about 100 μm, or equal to or less than about 90 μm, or equalto or less than about 80 μm, or equal to or less than about 70 μm, orequal to or less than about 60 μm, or equal to or less than about 50 μm,or equal to or less than about 40 μm, or equal to or less than about 30μm, or equal to or less than about 20 μm, or equal to or less than about10 μm.

In certain embodiments, the microfibrillated cellulose has a modal fibreparticle size ranging from about 0.1-500 μm. In certain embodiments, themicrofibrillated cellulose has a modal fibre particle size of at leastabout 0.5 μm, for example at least about 10 μm, or at least about 50 μm,or at least about 100 μm, or at least about 150 μm, or at least about200 μm, or at least about 300 μm, or at least about 400 μm.

Additionally or alternatively, the microfibrillated cellulose may have afibre steepness equal to or greater than about 10, as measured byMalvern. Fibre steepness (i.e., the steepness of the particle sizedistribution of the fibres) is determined by the following formula:

Steepness=100×(d ₃₀ /d ₇₀)

The microfibrillated cellulose may have a fibre steepness equal to orless than about 100. The microfibrillated cellulose may have a fibresteepness equal to or less than about 75, or equal to or less than about50, or equal to or less than about 40, or equal to or less than about30. The microfibrillated cellulose may have a fibre steepness from about20 to about 50, or from about 25 to about 40, or from about 25 to about35, or from about 30 to about 40.

The microfibrillated cellulose may, for example, be treated prior todewatering and/or drying. For example, one or more additives asspecified below (e.g. salt, sugar, glycol, urea, glycol, carboxymethylcellulose, guar gum, or a combination thereof as specified below) may beadded to the microfibrillated cellulose. For example, one or moreoligomers (e.g. with or without the additives specified above) may beadded to the microfibrillated cellulose. For example, one or moreinorganic particulate materials may be added to the microfibrillatedcellulose to improve dispersibility (e.g. talc or minerals having ahydrophobic surface-treatment such as a stearic acid surface-treatment(e.g. stearic acid treated calcium carbonate). The additives may, forexample, be suspended in low dielectric solvents. The microfibrillatedcellulose may, for example, be in an emulsion, for example an oil/wateremulsion, prior to dewatering and/or drying. The microfibrillatedcellulose may, for example, be in a masterbatch composition, for examplea polymer masterbatch composition and/or a high solids masterbatchcomposition, prior to dewatering and/or drying. The microfibrillatedcellulose may, for example, be a high solids composition (e.g. solidscontent equal to or greater than about 60 wt % or equal to or greaterthan about 70 wt % or equal to or greater than about 80 wt % or equal toor greater than about 90 wt % or equal to or greater than about 95 wt %or equal to or greater than about 98 wt % or equal to or greater thanabout 99 wt %) prior to dewatering and/or drying. Any combination of oneor more of the treatments may additionally or alternatively beapplicable to the microfibrillated cellulose after dewatering and dryingbut prior to or during re-dispersion.

The re-dispersed microfibrillated cellulose has a mechanical and/orphysical property which is closer to that of the microfibrillatedcellulose prior to drying or at least partial drying than it would havebeen but for drying in accordance with (i), (ii), (iii) or (iv) above.

In certain embodiments, the re-dispersed microfibrillated cellulose hasa mechanical and/or physical property which is closer to that of themicrofibrillated cellulose prior to drying or at least partial dryingthan it would have been but for drying in accordance with (i), (ii) or(iii).

The mechanical property may be any determinable mechanical propertyassociated with microfibrillated cellulose. For example, the mechanicalproperty may be a strength property, for example, tensile index. Tensileindex may be measured using a tensile tester. Any suitable method andapparatus may be used provided it is controlled in order to compare thetensile index of the microfibrillated cellulose before drying and afterre-dispersal. For example, the comparison should be conducted at equalconcentrations of microfibrillated cellulose, and any other additive orinorganic particulate material(s) which may be present. Tensile indexmay be expressed in any suitable units such as, for example, N.m/g orkN.m/kg.

The physical property may be any determinable physical propertyassociated with microfibrillated cellulose. For example, the physicalproperty may be viscosity. Viscosity may be measured using a viscometer.Any suitable method and apparatus may be used provided it is controlledin order to compare the viscosity of the microfibrillated celluloseprior to drying and after re-dispersal. For example, the comparisonshould be conducted at equal concentrations of microfibrillatedcellulose, and any other additive or inorganic particulate material(s)which may be present. In certain embodiments, the viscosity isBrookfield viscosity, with units of mPa·s.

In certain embodiments, the tensile index and/or viscosity of there-dispersed microfibrillated cellulose is at least about 25% of thetensile index and/or viscosity of the aqueous composition ofmicrofibrillated cellulose prior to drying, for example, at least about30%, or at least about 35%, or at least about 40%, or at least 45%, orat least about 50%, or at least about 55%, or at least about 60%, or atleast about 65%, or at least about 70%, or at least about 75%, or atleast about 80% of the tensile index and/or viscosity of themicrofibrillated cellulose prior to drying.

For example, if the tensile index of the microfibrillated celluloseprior to drying was 8 N.m/g, then a tensile index of at least 50% ofthis value would be 4 N.m/g.

In certain embodiments, the tensile index of the re-dispersedmicrofibrillated cellulose is at least about 25% of the tensile index ofthe aqueous composition of microfibrillated cellulose prior to drying,for example, at least about 30%, or at least about 35%, or at leastabout 40%, or at least 45%, or at least about 50%, or at least about55%, or at least about 60%, or at least about 65%, or at least about70%, or at least about 75%, or at least about 80% of the tensile indexof the microfibrillated cellulose prior to drying.

In certain embodiments, the viscosity of the re-dispersedmicrofibrillated cellulose is at least about 25% of the viscosity of theaqueous composition of microfibrillated cellulose prior to drying, forexample, at least about 30%, or at least about 35%, or at least about40%, or at least 45%, or at least about 50%, or at least about 55%, orat least about 60%, or at least about 65%, or at least about 70%, or atleast about 75%, or at least about 80% of the viscosity of themicrofibrillated cellulose prior to drying.

In certain embodiments, inorganic particulate material and/or anadditive other than inorganic particulate material is present during thedewatering and drying. The inorganic particulate material and/oradditive may be added at any stage prior to dewatering and drying. Forexample, the inorganic particulate material and/or additive may be addedduring manufacture of the aqueous composition comprisingmicrofibrillated cellulose, following manufacture of the aqueouscomposition comprising microfibrillated cellulose, or both. In certainembodiments, the inorganic particulate material is incorporated duringmanufacture of the microfibrillated cellulose (for example, byco-processing, e.g., co-grinding, as described here) and the additiveother than inorganic particulate material is added following manufactureof the aqueous composition comprising microfibrillated cellulose. Incertain embodiments, additional inorganic particulate material (whichmay be the same or different than the inorganic particulate added duringmanufacture of the microfibrillated cellulose) may be added followingmanufacture of the microfibrillated cellulose, for example,contemporaneously with the addition of additive other than inorganicparticulate material. In certain embodiments, the microfibrillatedcellulose of the aqueous composition has a fibre steepness of from 20 to50. Details of the inorganic particulate material, additives and amountsthereof are described below.

In a further aspect, the method of re-dispersing microfibrillatedcellulose comprises re-dispersing dried or at least partially driedmicrofibrillated cellulose in a liquid medium and in the presence of anadditive other than inorganic particulate material which enhances amechanical and/or physical property of the re-dispersedmicrofibrillated. The microfibrillated cellulose prior to being to bedried or at least partially dried has a fibre steepness of from 20 to50.

In yet a further aspect, the method of re-dispersing microfibrillatedcellulose comprises re-dispersing dried or at least partially driedmicrofibrillated cellulose in a liquid medium and in the presence of acombination of inorganic particulate materials, wherein the combinationof inorganic particulate materials enhances a mechanical and/or physicalproperty of the re-dispersed microfibrillated. In certain embodiments,the combination of inorganic particulate materials comprises calciumcarbonate and a platy mineral, for example, a platy kaolin, or talc.

In certain embodiments, the additive, when present, is a salt, sugar,glycol, urea, glycol, carboxymethyl cellulose, guar gum, or acombination thereof.

In certain embodiments, the additive, when present, is a salt, sugar,glycol, urea, glycol, guar gum, or a combination thereof.

In certain embodiments, sugar is selected from monosaccharides (e.g.glucose, fructose, galactose), disaccharides (e.g. lactose, maltose,sucrose), oilgosacchardies (chains of 50 or less units of one or moremonosaccharides) polysaccharides and combinations thereof.

In certain embodiments, the salt is an alkali metal or alkaline earthmetal chloride, for example, sodium, potassium, magnesium and/or calciumchloride. In certain embodiments, the salt comprises or is sodiumchloride.

In certain embodiments, the glyclol is and alkylene glycol, for example,selected from ethylene, propylene and butylene glycol, and combinationsthereof. In certain embodiments, the glycol comprises or is ethyleneglycol.

In certain embodiments, the additive comprises or is urea.

In certain embodiments, the additive comprises or is guar gum.

In certain embodiments, the additive comprises or is carboxymethylcellulose. In certain embodiments, the additive is not carboxymethylcellulose.

In certain embodiments, the microfibrillated cellulose prior to dryingor at least partially drying is not acetylsed. In certain embodiments,the microfibrillated cellulose prior to drying or at least partiallydrying is not subjected to acetylation.

The inorganic particulate material may be added at one or more of thefollowing stages: (i) prior to or during manufacture of the aqueouscomposition comprising microfibrillated cellulose; (ii) followingmanufacture of the aqueous composition comprising microfibrillatedcellulose; (iii) during dewatering of the aqueous composition ofmicrofibrillated cellulose; (iv) during drying of the aqueouscomposition of microfibrillated cellulose; and (v) prior to or duringre-dispersing of the dried or at least partially dried microfibrillatedcellulose.

The re-dispersed microfibrillated cellulose has a mechanical and/orphysical property which is closer to that of the microfibrillatedcellulose prior to drying and re-dispersal than it would have been butfor the presence of the inorganic particulate and/or additive. In otherwords, the presence of the inorganic particulate material and/oradditive other than inorganic particulate material enhances a mechanicaland/or physical property of the re-dispersed microfibrillated.

In certain embodiments, the re-dispersed microfibrillated cellulose hasa mechanical and/or physical property which is closer to that of themicrofibrillated cellulose prior to drying or at least partial dryingthan it would have been but for the presence of the inorganicparticulate material and/or additive.

As described above, the mechanical property may be any determinablemechanical property associated with microfibrillated cellulose. Forexample, the mechanical property may be a strength property, forexample, tensile index. Tensile index may be measured using a tensiletester. Any suitable method and apparatus may be used provided it iscontrolled in order to compare the tensile index of the microfibrillatedcellulose before drying and after re-dispersal. For example, thecomparison should be conducted at equal concentrations ofmicrofibrillated cellulose, and any other additive or inorganicparticulate material(s) which may be present. Tensile index may beexpressed in any suitable units such as, for example, N.m/g or kN.m/kg.

The physical property may be any determinable physical propertyassociated with microfibrillated cellulose. For example, the physicalproperty may be viscosity. Viscosity may be measured using a viscometer.Any suitable method and apparatus may be used provided it is controlledin order to compare the viscosity of the microfibrillated celluloseprior to drying and after re-dispersal. For example, the comparisonshould be conducted at equal concentrations of microfibrillatedcellulose, and any other additive or inorganic particulate material(s)which may be present. In certain embodiments, the viscosity isBrookfield viscosity, with units of mPa·s.

In certain embodiments, the tensile index and/or viscosity of there-dispersed microfibrillated cellulose is at least about 25% of thetensile index and/or viscosity of the aqueous composition ofmicrofibrillated cellulose prior to drying, for example, at least about30%, or at least about 35%, or at least about 40%, or at least 45%, orat least about 50%, or at least about 55%, or at least about 60%, or atleast about 65%, or at least about 70%, or at least about 75%, or atleast about 80% of the tensile index and/or viscosity of themicrofibrillated cellulose prior to drying.

For example, if the tensile index of the microfibrillated celluloseprior to drying was 8 N.m/g, then a tensile index of at least 50% ofthis value would be 4 N.m/g.

In certain embodiments, the tensile index of the re-dispersedmicrofibrillated cellulose is at least about 25% of the tensile index ofthe aqueous composition of microfibrillated cellulose prior to drying,for example, at least about 30%, or at least about 35%, or at leastabout 40%, or at least 45%, or at least about 50%, or at least about55%, or at least about 60%, or at least about 65%, or at least about70%, or at least about 75%, or at least about 80% of the tensile indexof the microfibrillated cellulose prior to drying.

In certain embodiments, the viscosity of the re-dispersedmicrofibrillated cellulose is at least about 25% of the viscosity of theaqueous composition of microfibrillated cellulose prior to drying, forexample, at least about 30%, or at least about 35%, or at least about40%, or at least 45%, or at least about 50%, or at least about 55%, orat least about 60%, or at least about 65%, or at least about 70%, or atleast about 75%, or at least about 80% of the viscosity of themicrofibrillated cellulose prior to drying.

The inorganic particulate material and/or additive, when present, arepresent in sufficient amounts in order to enhance the re-dispersibilityof the microfibrillated cellulose, i.e., enhances a mechanical and/orphysical property of the re-dispersed microfibrillated.

Based on the total weight of the aqueous composition comprisingmicrofibrillated cellulose (including inorganic particulate whenpresent) prior to drying, the additive may be added in an amount of fromabout 0.1 wt. % to about 200 wt. %, from about 0.1 wt. % to about 100wt. %, from about 0.1 wt. % to about wt. 80%, from about 0.1 wt. % toabout wt. 60%, from about 0.1 wt. % to about wt. 40%, from about 0.1 wt.% to about 20 wt. %, or from about 0.25 wt. % to about 15 wt. %, or fromabout 0.5 wt. % to about 10 wt. %, or from about 0.5 wt. % to about 7.5wt. %, or from about 0.5 wt. % to about 5 wt. %, or from about 0.5 wt. %to about 4 wt. %, or from about 9.5 wt. % to about 4 wt. %, or fromabout 1 wt. % to about 3 wt. %.

The aqueous composition comprising microfibrillated cellulose andoptional inorganic particulate material may have a solids content of upto about 50 wt. % prior to drying, for example, up to about 40 wt. %, orup to about 30 wt. %, or up to about 20 wt. %, or up to about 15 wt. %,or up to about 10 wt. %, or up to about 5 wt. %, or up to about 4 wt. %,or up to about 3 wt. %, or up to about 2 wt. %, or up to about 2 wt. %.

Based on the solids content of the aqueous composition microfibrillatedcellulose prior to drying, the inorganic particulate may constitute upto about 99% of the total solids content, for example, up to about 90%,or up to about 80 wt. %, or up to about 70 wt. %, or up to about 60 wt.%, or up to about 50 wt. %, or up to about 40%, or up to about 30%, orup to about 20%, or up to about 10%, or up to about 5% of the totalsolids content.

In certain embodiments, the weight ratio of inorganic particulate tomicrofibrillated cellulose in the aqueous composition is from about 10:1to about 1:2, for example, from about 8:1 to about 1:1, or from about6:1 to about 3:2, or from about 5:1 to about 2:1, or from about 5:1 toabout 3:1, or about 4:1 to about 3:1, or about 4:1.

In certain embodiments, the aqueous composition of microfibrillatedcellulose prior to drying or at least partially drying has a solidscontent of up to about 20 wt. %, optionally wherein up to about 80% ofthe solids is inorganic particulate material.

In certain embodiments, the aqueous composition is substantially free ofinorganic particulate material prior to drying.

The inorganic particulate material may, for example, be an alkalineearth metal carbonate or sulphate, such as calcium carbonate, magnesiumcarbonate, dolomite, gypsum, a hydrous kandite clay such as kaolin,halloysite or ball clay, an anhydrous (calcined) kandite clay such asmetakaolin or fully calcined kaolin, talc, mica, huntite,hydromagnesite, ground glass, perlite or diatomaceous earth, orwollastonite, or titanium dioxide, or magnesium hydroxide, or aluminiumtrihydrate, lime, graphite, or combinations thereof.

In certain embodiments, the inorganic particulate material comprises oris calcium carbonate, magnesium carbonate, dolomite, gypsum, ananhydrous kandite clay, perlite, diatomaceous earth, wollastonite,magnesium hydroxide, or aluminium trihydrate, titanium dioxide orcombinations thereof.

In certain embodiments, the inorganic particulate material may be asurface-treated inorganic particulate material. For instance, theinorganic particulate material may be treated with a hydrophobizingagent, such as a fatty acid or salt thereof. For example, the inorganicparticulate material may be a stearic acid treated calcium carbonate.

An exemplary inorganic particulate material for use in the presentinvention is calcium carbonate. Hereafter, the invention may tend to bediscussed in terms of calcium carbonate, and in relation to aspectswhere the calcium carbonate is processed and/or treated. The inventionshould not be construed as being limited to such embodiments.

The particulate calcium carbonate used in the present invention may beobtained from a natural source by grinding. Ground calcium carbonate(GCC) is typically obtained by crushing and then grinding a mineralsource such as chalk, marble or limestone, which may be followed by aparticle size classification step, in order to obtain a product havingthe desired degree of fineness. Other techniques such as bleaching,flotation and magnetic separation may also be used to obtain a producthaving the desired degree of fineness and/or colour. The particulatesolid material may be ground autogenously, i.e. by attrition between theparticles of the solid material themselves, or, alternatively, in thepresence of a particulate grinding medium comprising particles of adifferent material from the calcium carbonate to be ground. Theseprocesses may be carried out with or without the presence of adispersant and biocides, which may be added at any stage of the process.

Precipitated calcium carbonate (PCC) may be used as the source ofparticulate calcium carbonate in the present invention, and may beproduced by any of the known methods available in the art. TAPPIMonograph Series No 30, “Paper Coating Pigments”, pages 34-35 describesthe three main commercial processes for preparing precipitated calciumcarbonate which is suitable for use in preparing products for use in thepaper industry, but may also be used in the practice of the presentinvention. In all three processes, a calcium carbonate feed material,such as limestone, is first calcined to produce quicklime, and thequicklime is then slaked in water to yield calcium hydroxide or milk oflime. In the first process, the milk of lime is directly carbonated withcarbon dioxide gas. This process has the advantage that no by-product isformed, and it is relatively easy to control the properties and purityof the calcium carbonate product. In the second process the milk of limeis contacted with soda ash to produce, by double decomposition, aprecipitate of calcium carbonate and a solution of sodium hydroxide. Thesodium hydroxide may be substantially completely separated from thecalcium carbonate if this process is used commercially. In the thirdmain commercial process the milk of lime is first contacted withammonium chloride to give a calcium chloride solution and ammonia gas.The calcium chloride solution is then contacted with soda ash to produceby double decomposition precipitated calcium carbonate and a solution ofsodium chloride. The crystals can be produced in a variety of differentshapes and sizes, depending on the specific reaction process that isused. The three main forms of PCC crystals are aragonite, rhombohedraland scalenohedral (e.g., calcite), all of which are suitable for use inthe present invention, including mixtures thereof.

In certain embodiments, the PCC may be formed during the process ofproducing microfibrillated cellulose.

Wet grinding of calcium carbonate involves the formation of an aqueoussuspension of the calcium carbonate which may then be ground, optionallyin the presence of a suitable dispersing agent. Reference may be madeto, for example, EP-A-614948 (the contents of which are incorporated byreference in their entirety) for more information regarding the wetgrinding of calcium carbonate.

When the inorganic particulate material of the present invention isobtained from naturally occurring sources, it may be that some mineralimpurities will contaminate the ground material. For example, naturallyoccurring calcium carbonate can be present in association with otherminerals. Thus, in some embodiments, the inorganic particulate materialincludes an amount of impurities. In general, however, the inorganicparticulate material used in the invention will contain less than about5% by weight, or less than about 1% by weight, of other mineralimpurities.

The inorganic particulate material may have a particle size distributionin which at least about 10% by weight of the particles have an e.s.d ofless than 2 μm, for example, at least about 20% by weight, or at leastabout 30% by weight, or at least about 40% by weight, or at least about50% by weight, or at least about 60% by weight, or at least about 70% byweight, or at least about 80% by weight, or at least about 90% byweight, or at least about 95% by weight, or about 100% of the particleshave an e.s.d of less than 2 μm.

In another embodiment, the inorganic particulate material has a particlesize distribution, as measured using a Malvern Mastersizer S machine, inwhich at least about 10% by volume of the particles have an e.s.d ofless than 2 μm, for example, at least about 20% by volume, or at leastabout 30% by volume, or at least about 40% by volume, or at least about50% by volume, or at least about 60% by volume, or at least about 70% byvolume, or at least about 80% by volume, or at least about 90% byvolume, or at least about 95% by volume, or about 100% of the particlesby volume have an e.s.d of less than 2 μm.

Details of the procedure used to characterise the particle sizedistributions of mixtures of inorganic particle material andmicrofibrillated cellulose using a Malvern Mastersizer S machine areprovided below.

In certain embodiments, the inorganic particulate material is orcomprises kaolin clay. Hereafter, this section of the specification maytend to be discussed in terms of kaolin, and in relation to aspectswhere the kaolin is processed and/or treated. The invention should notbe construed as being limited to such embodiments. Thus, in someembodiments, kaolin is used in an unprocessed form.

Kaolin clay used in this invention may be a processed material derivedfrom a natural source, namely raw natural kaolin clay mineral. Theprocessed kaolin clay may typically contain at least about 50% by weightkaolinite. For example, most commercially processed kaolin clays containgreater than about 75% by weight kaolinite and may contain greater thanabout 90%, in some cases greater than about 95% by weight of kaolinite.

Kaolin clay used in the present invention may be prepared from the rawnatural kaolin clay mineral by one or more other processes which arewell known to those skilled in the art, for example by known refining orbeneficiation steps.

For example, the clay mineral may be bleached with a reductive bleachingagent, such as sodium hydrosulfite. If sodium hydrosulfite is used, thebleached clay mineral may optionally be dewatered, and optionally washedand again optionally dewatered, after the sodium hydrosulfite bleachingstep.

The clay mineral may be treated to remove impurities, e. g. byflocculation, flotation, or magnetic separation techniques well known inthe art. Alternatively the clay mineral used in the first aspect of theinvention may be untreated in the form of a solid or as an aqueoussuspension.

The process for preparing the particulate kaolin clay may also includeone or more comminution steps, e.g., grinding or milling. Lightcomminution of a coarse kaolin is used to give suitable delaminationthereof. The comminution may be carried out by use of beads or granulesof a plastic (e. g. nylon), sand or ceramic grinding or milling aid. Thecoarse kaolin may be refined to remove impurities and improve physicalproperties using well known procedures. The kaolin clay may be treatedby a known particle size classification procedure, e.g., screening andcentrifuging (or both), to obtain particles having a desired d₅₀ valueor particle size distribution.

In certain embodiments, the inorganic particulate material is orcomprises a platy mineral, for example, kaolin and/or talc, optionallyin combination with another inorganic particulate material, such as, forexample, calcium carbonate.

By ‘platy’ kaolin is meant kaolin a kaolin product having a high shapefactor. A platy kaolin has a shape factor from about 20 to less thanabout 60. A hyper-platy kaolin has a shape factor from about 60 to 100or even greater than 100. “Shape factor”, as used herein, is a measureof the ratio of particle diameter to particle thickness for a populationof particles of varying size and shape as measured using the electricalconductivity methods, apparatuses, and equations described in U.S. Pat.No. 5,576,617, which is incorporated herein by reference. As thetechnique for determining shape factor is further described in the '617patent, the electrical conductivity of a composition of an aqueoussuspension of orientated particles under test is measured as thecomposition flows through a vessel. Measurements of the electricalconductivity are taken along one direction of the vessel and alonganother direction of the vessel transverse to the first direction. Usingthe difference between the two conductivity measurements, the shapefactor of the particulate material under test is determined.

In certain embodiments, the inorganic particulate material is orcomprises talc, optionally in combination with another inorganicparticulate material, such as, for example, calcium carbonate.

In certain embodiments, the inorganic particulate material is calciumcarbonate, which may be surface treated, and the aqueous compositionfurther comprises one or more of the additives other than inorganicparticulate material as described herein.

In certain embodiments, the inorganic particulate material is kaolin,for example, a platy or hyper play kaolin, which may be surface treated,and the aqueous composition further comprises one or more of theadditives other than inorganic particulate material as described herein.

In certain embodiments, the inorganic particulate material is talc,which may be surface treated, and the aqueous composition furthercomprises one or more of the additives other than inorganic particulatematerial as described herein.

In certain embodiments, the aqueous composition comprisingmicrofibrillated cellulose is free of inorganic particulate material,and the aqueous composition further comprises one or more of theadditives other than inorganic particulate material as described herein.

The various methods described herein provide for the manufacture ofre-dispersed microfibrillated cellulose having advantageous properties.

Thus, in a further aspect, there is provided a composition comprisingre-dispersed microfibrillated cellulose dispersed in a liquid medium andwhich is obtainable by a method according to any one of method aspectsdescribed herein, and having, at a comparable concentration, a tensileindex and/or viscosity which is at least 50% of the tensile index and/orviscosity of the aqueous composition of microfibrillated cellulose priorto drying, wherein either (i) the microfibrillated cellulose of theaqueous composition has a fibre steepness of from 20 to 50, and/or (ii)the aqueous composition of microfibrillated cellulose comprisesinorganic particulate material, and optionally further comprises anadditive other than inorganic particulate material.

The re-dispersed microfibrillated cellulose may be used, in an article,product, or composition, for example, paper, paperboard, polymericarticles, paints, and the like.

Methods of Manufacturing Microfibrillated Cellulose and OptionalInorganic Particulate Material

In certain embodiments, the microfibrillated cellulose may be preparedin the presence of or in the absence of the inorganic particulatematerial.

The microfibrillated cellulose is derived from fibrous substratecomprising cellulose. The fibrous substrate comprising cellulose may bederived from any suitable source, such as wood, grasses (e.g.,sugarcane, bamboo) or rags (e.g., textile waste, cotton, hemp or flax).The fibrous substrate comprising cellulose may be in the form of a pulp(i.e., a suspension of cellulose fibres in water), which may be preparedby any suitable chemical or mechanical treatment, or combinationthereof. For example, the pulp may be a chemical pulp, or achemithermomechanical pulp, or a mechanical pulp, or a recycled pulp, ora papermill broke, or a papermill waste stream, or waste from apapermill, or a dissolving pulp, kenaf pulp, market pulp, partiallycarboxymethylated pulp, abaca pulp, hemlock pulp, birch pulp, grasspulp, bamboo pulp, palm pulp, peanut shell, or a combination thereof.The cellulose pulp may be beaten (for example in a Valley beater) and/orotherwise refined (for example, processing in a conical or platerefiner) to any predetermined freeness, reported in the art as Canadianstandard freeness (CSF) in cm³. CSF means a value for the freeness ordrainage rate of pulp measured by the rate that a suspension of pulp maybe drained. For example, the cellulose pulp may have a Canadian standardfreeness of about 10 cm³ or greater prior to being microfibrillated. Thecellulose pulp may have a CSF of about 700 cm³ or less, for example,equal to or less than about 650 cm³, or equal to or less than about 600cm³, or equal to or less than about 550 cm³, or equal to or less thanabout 500 cm³, or equal to or less than about 450 cm³, or equal to orless than about 400 cm³, or equal to or less than about 350 cm³, orequal to or less than about 300 cm³, or equal to or less than about 250cm³, or equal to or less than about 200 cm³, or equal to or less thanabout 150 cm³, or equal to or less than about 100 cm³, or equal to orless than about 50 cm³. The cellulose pulp may then be dewatered bymethods well known in the art, for example, the pulp may be filteredthrough a screen in order to obtain a wet sheet comprising at leastabout 10% solids, for example at least about 15% solids, or at leastabout 20% solids, or at least about 30% solids, or at least about 40%solids. The pulp may be utilised in an unrefined state, that is to say,without being beaten or dewatered, or otherwise refined.

In certain embodiments, the pulp may be beaten in the presence of aninorganic particulate material, such as calcium carbonate.

For preparation of microfibrillated cellulose, the fibrous substratecomprising cellulose may be added to a grinding vessel or homogenizer ina dry state. For example, a dry paper broke may be added directly to agrinder vessel. The aqueous environment in the grinder vessel will thenfacilitate the formation of a pulp.

The step of microfibrillating may be carried out in any suitableapparatus, including but not limited to a refiner. In one embodiment,the microfibrillating step is conducted in a grinding vessel underwet-grinding conditions. In another embodiment, the microfibrillatingstep is carried out in a homogenizer. Each of these embodiments isdescribed in greater detail below.

-   -   wet-grinding

The grinding is suitably performed in a conventional manner. Thegrinding may be an attrition grinding process in the presence of aparticulate grinding medium, or may be an autogenous grinding process,i.e., one in the absence of a grinding medium. By grinding medium ismeant a medium other than the inorganic particulate material which incertain embodiments may be co-ground with the fibrous substratecomprising cellulose.

The particulate grinding medium, when present, may be of a natural or asynthetic material. The grinding medium may, for example, compriseballs, beads or pellets of any hard mineral, ceramic or metallicmaterial. Such materials may include, for example, alumina, zirconia,zirconium silicate, aluminium silicate or the mullite-rich materialwhich is produced by calcining kaolinitic clay at a temperature in therange of from about 1300° C. to about 1800° C. For example, in someembodiments a Carbolite® grinding media is used. Alternatively,particles of natural sand of a suitable particle size may be used.

In other embodiments, hardwood grinding media (e.g., woodflour) may beused.

Generally, the type of and particle size of grinding medium to beselected for use in the invention may be dependent on the properties,such as, e.g., the particle size of, and the chemical composition of,the feed suspension of material to be ground. In some embodiments, theparticulate grinding medium comprises particles having an averagediameter in the range of from about 0.1 mm to about 6.0 mm, for example,in the range of from about 0.2 mm to about 4.0 mm. The grinding medium(or media) may be present in an amount up to about 70% by volume of thecharge. The grinding media may be present in amount of at least about10% by volume of the charge, for example, at least about 20% by volumeof the charge, or at least about 30% by volume of the charge, or atleast about 40% by volume of the charge, or at least about 50% by volumeof the charge, or at least about 60% by volume of the charge.

The grinding may be carried out in one or more stages. For example, acoarse inorganic particulate material may be ground in the grindervessel to a predetermined particle size distribution, after which thefibrous material comprising cellulose is added and the grindingcontinued until the desired level of microfibrillation has beenobtained.

The inorganic particulate material may be wet or dry ground in theabsence or presence of a grinding medium. In the case of a wet grindingstage, the coarse inorganic particulate material is ground in an aqueoussuspension in the presence of a grinding medium.

In one embodiment, the mean particle size (d₅₀) of the inorganicparticulate material is reduced during the co-grinding process. Forexample, the d₅₀ of the inorganic particulate material may be reduced byat least about 10% (as measured by a Malvern Mastersizer S machine), forexample, the d₅₀ of the inorganic particulate material may be reduced byat least about 20%, or reduced by at least about 30%, or reduced by atleast about 50%, or reduced by at least about 50%, or reduced by atleast about 60%, or reduced by at least about 70%, or reduced by atleast about 80%, or reduced by at least about 90%. For example, aninorganic particulate material having a d₅₀ of 2.5 μm prior toco-grinding and a d₅₀ of 1.5 μm post co-grinding will have been subjectto a 40% reduction in particle size. In certain embodiments, the meanparticle size of the inorganic particulate material is not significantlyreduced during the co-grinding process. By ‘not significantly reduced’is meant that the d₅₀ of the inorganic particulate material is reducedby less than about 10%, for example, the d₅₀ of the inorganicparticulate material is reduced by less than about 5%.

The fibrous substrate comprising cellulose may be microfibrillated,optionally in the presence of an inorganic particulate material, toobtain microfibrillated cellulose having a d₅₀ ranging from about 5 toμm about 500 μm, as measured by laser light scattering. The fibroussubstrate comprising cellulose may be microfibrillated, optionally inthe presence of an inorganic particulate material, to obtainmicrofibrillated cellulose having a d₅₀ of equal to or less than about400 μm, for example equal to or less than about 300 μm, or equal to orless than about 200 μm, or equal to or less than about 150 μm, or equalto or less than about 125 μm, or equal to or less than about 100 μm, orequal to or less than about 90 μm, or equal to or less than about 80 μm,or equal to or less than about 70 μm, or equal to or less than about 60μm, or equal to or less than about 50 μm, or equal to or less than about40 μm, or equal to or less than about 30 μm, or equal to or less thanabout 20 μm, or equal to or less than about 10 μm.

The fibrous substrate comprising cellulose may be microfibrillated,optionally in the presence of an inorganic particulate material, toobtain microfibrillated cellulose having a modal fibre particle sizeranging from about 0.1-500 μm and a modal inorganic particulate materialparticle size ranging from 0.25-20 μm. The fibrous substrate comprisingcellulose may be microfibrillated, optionally in the presence of aninorganic particulate material to obtain microfibrillated cellulosehaving a modal fibre particle size of at least about 0.5 μm, for exampleat least about 10 μm, or at least about 50 μm, or at least about 100 μm,or at least about 150 μm, or at least about 200 μm, or at least about300 μm, or at least about 400 μm.

The fibrous substrate comprising cellulose may be microfibrillated,optionally in the presence of an inorganic particulate material, toobtain microfibrillated cellulose having a fibre steepness, as describedabove.

The grinding may be performed in a grinding vessel, such as a tumblingmill (e.g., rod, ball and autogenous), a stirred mill (e.g., SAM orIsaMill), a tower mill, a stirred media detritor (SMD), or a grindingvessel comprising rotating parallel grinding plates between which thefeed to be ground is fed.

In one embodiment, the grinding vessel is a tower mill. The tower millmay comprise a quiescent zone above one or more grinding zones. Aquiescent zone is a region located towards the top of the interior oftower mill in which minimal or no grinding takes place and comprisesmicrofibrillated cellulose and optional inorganic particulate material.The quiescent zone is a region in which particles of the grinding mediumsediment down into the one or more grinding zones of the tower mill.

The tower mill may comprise a classifier above one or more grindingzones. In an embodiment, the classifier is top mounted and locatedadjacent to a quiescent zone. The classifier may be a hydrocyclone.

The tower mill may comprise a screen above one or more grind zones. Inan embodiment, a screen is located adjacent to a quiescent zone and/or aclassifier. The screen may be sized to separate grinding media from theproduct aqueous suspension comprising microfibrillated cellulose andoptional inorganic particulate material and to enhance grinding mediasedimentation.

In an embodiment, the grinding is performed under plug flow conditions.Under plug flow conditions the flow through the tower is such that thereis limited mixing of the grinding materials through the tower. Thismeans that at different points along the length of the tower mill theviscosity of the aqueous environment will vary as the fineness of themicrofibrillated cellulose increases. Thus, in effect, the grindingregion in the tower mill can be considered to comprise one or moregrinding zones which have a characteristic viscosity. A skilled personin the art will understand that there is no sharp boundary betweenadjacent grinding zones with respect to viscosity.

In an embodiment, water is added at the top of the mill proximate to thequiescent zone or the classifier or the screen above one or moregrinding zones to reduce the viscosity of the aqueous suspensioncomprising microfibrillated cellulose and optional inorganic particulatematerial at those zones in the mill. By diluting the productmicrofibrillated cellulose and optional inorganic particulate materialat this point in the mill it has been found that the prevention ofgrinding media carry over to the quiescent zone and/or the classifierand/or the screen is improved. Further, the limited mixing through thetower allows for processing at higher solids lower down the tower anddilute at the top with limited backflow of the dilution water back downthe tower into the one or more grinding zones. Any suitable amount ofwater which is effective to dilute the viscosity of the product aqueoussuspension comprising microfibrillated cellulose and optional inorganicparticulate material may be added. The water may be added continuouslyduring the grinding process, or at regular intervals, or at irregularintervals.

In another embodiment, water may be added to one or more grinding zonesvia one or more water injection points positioned along the length ofthe tower mill, or each water injection point being located at aposition which corresponds to the one or more grinding zones.Advantageously, the ability to add water at various points along thetower allows for further adjustment of the grinding conditions at any orall positions along the mill.

The tower mill may comprise a vertical impeller shaft equipped with aseries of impeller rotor disks throughout its length. The action of theimpeller rotor disks creates a series of discrete grinding zonesthroughout the mill.

In another embodiment, the grinding is performed in a screened grinder,such as a stirred media detritor. The screened grinder may comprise oneor more screen(s) having a nominal aperture size of at least about 250μm, for example, the one or more screens may have a nominal aperturesize of at least about 300 μm, or at least about 350 μm, or at leastabout 400 μm, or at least about 450 μm, or at least about 500 μm, or atleast about 550 μm, or at least about 600 μm, or at least about 650 μm,or at least about 700 μm, or at least about 750 μm, or at least about800 μm, or at least about 850 μm, or at or least about 900 μm, or atleast about 1000 μm.

The screen sizes noted immediately above are applicable to the towermill embodiments described above.

As noted above, the grinding may be performed in the presence of agrinding medium. In an embodiment, the grinding medium is a coarse mediacomprising particles having an average diameter in the range of fromabout 1 mm to about 6 mm, for example about 2 mm, or about 3 mm, orabout 4 mm, or about 5 mm.

In another embodiment, the grinding media has a specific gravity of atleast about 2.5, for example, at least about 3, or at least about 3.5,or at least about 4.0, or at least about 4.5, or least about 5.0, or atleast about 5.5, or at least about 6.0.

In another embodiment, the grinding media comprises particles having anaverage diameter in the range of from about 1 mm to about 6 mm and has aspecific gravity of at least about 2.5.

In another embodiment, the grinding media comprises particles having anaverage diameter of about 3 mm and specific gravity of about 2.7.

As described above, the grinding medium (or media) may present in anamount up to about 70% by volume of the charge. The grinding media maybe present in amount of at least about 10% by volume of the charge, forexample, at least about 20% by volume of the charge, or at least about30% by volume of the charge, or at least about 40% by volume of thecharge, or at least about 50% by volume of the charge, or at least about60% by volume of the charge.

In one embodiment, the grinding medium is present in amount of about 50%by volume of the charge.

By ‘charge’ is meant the composition which is the feed fed to thegrinder vessel. The charge includes of water, grinding media, fibroussubstrate comprising cellulose and optional inorganic particulatematerial, and any other optional additives as described herein.

The use of a relatively coarse and/or dense media has the advantage ofimproved (i.e., faster) sediment rates and reduced media carry overthrough the quiescent zone and/or classifier and/or screen(s).

A further advantage in using relatively coarse grinding media is thatthe mean particle size (d₅₀) of the inorganic particulate material maynot be significantly reduced during the grinding process such that theenergy imparted to the grinding system is primarily expended inmicrofibrillating the fibrous substrate comprising cellulose.

A further advantage in using relatively coarse screens is that arelatively coarse or dense grinding media can be used in themicrofibrillating step. In addition, the use of relatively coarsescreens (i.e., having a nominal aperture of least about 250 μm) allows arelatively high solids product to be processed and removed from thegrinder, which allows a relatively high solids feed (comprising fibroussubstrate comprising cellulose and inorganic particulate material) to beprocessed in an economically viable process. As discussed below, it hasbeen found that a feed having a high initial solids content is desirablein terms of energy sufficiency. Further, it has also been found thatproduct produced (at a given energy) at lower solids has a coarserparticle size distribution.

The grinding may be performed in a cascade of grinding vessels, one ormore of which may comprise one or more grinding zones. For example, thefibrous substrate comprising cellulose and the inorganic particulatematerial may be ground in a cascade of two or more grinding vessels, forexample, a cascade of three or more grinding vessels, or a cascade offour or more grinding vessels, or a cascade of five or more grindingvessels, or a cascade of six or more grinding vessels, or a cascade ofseven or more grinding vessels, or a cascade of eight or more grindingvessels, or a cascade of nine or more grinding vessels in series, or acascade comprising up to ten grinding vessels. The cascade of grindingvessels may be operatively linked in series or parallel or a combinationof series and parallel. The output from and/or the input to one or moreof the grinding vessels in the cascade may be subjected to one or morescreening steps and/or one or more classification steps.

The circuit may comprise a combination of one or more grinding vesselsand homegenizer.

In an embodiment the grinding is performed in a closed circuit. Inanother embodiment, the grinding is performed in an open circuit. Thegrinding may be performed in batch mode. The grinding may be performedin a re-circulating batch mode.

As described above, the grinding circuit may include a pre-grinding stepin which coarse inorganic particulate ground in a grinder vessel to apredetermined particle size distribution, after which fibrous materialcomprising cellulose is combined with the pre-ground inorganicparticulate material and the grinding continued in the same or differentgrinding vessel until the desired level of microfibrillation has beenobtained.

As the suspension of material to be ground may be of a relatively highviscosity, a suitable dispersing agent may be added to the suspensionprior to grinding. The dispersing agent may be, for example, a watersoluble condensed phosphate, polysilicic acid or a salt thereof, or apolyelectrolyte, for example a water soluble salt of a poly(acrylicacid) or of a poly(methacrylic acid) having a number average molecularweight not greater than 80,000. The amount of the dispersing agent usedwould generally be in the range of from 0.1 to 2.0% by weight, based onthe weight of the dry inorganic particulate solid material. Thesuspension may suitably be ground at a temperature in the range of from4° C. to 100° C.

Other additives which may be included during the microfibrillation stepinclude: carboxymethyl cellulose, amphoteric carboxymethyl cellulose,oxidising agents, 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO), TEMPOderivatives, and wood degrading enzymes.

The pH of the suspension of material to be ground may be about 7 orgreater than about 7 (i.e., basic), for example, the pH of thesuspension may be about 8, or about 9, or about 10, or about 11. The pHof the suspension of material to be ground may be less than about 7(i.e., acidic), for example, the pH of the suspension may be about 6, orabout 5, or about 4, or about 3. The pH of the suspension of material tobe ground may be adjusted by addition of an appropriate amount of acidor base. Suitable bases included alkali metal hydroxides, such as, forexample NaOH. Other suitable bases are sodium carbonate and ammonia.Suitable acids included inorganic acids, such as hydrochloric andsulphuric acid, or organic acids. An exemplary acid is orthophosphoricacid.

The amount of inorganic particulate material, when present, andcellulose pulp in the mixture to be co-ground may be varied in order toproduce a slurry which is suitable for drying and re-dispersal, and/orwhich may be further modified, e.g., with additional of furtherinorganic particulate material and/or additive other than inorganicparticulate material, to produce a slurry which is suitable for dryingor at least partially drying, optional transport to another location,re-dispersal and use in the manufacture of an article, product orcomposition.

Homogenizing

Microfibrillation of the fibrous substrate comprising cellulose may beeffected under wet conditions, optionally, in the presence of theinorganic particulate material, by a method in which the mixture ofcellulose pulp and optional inorganic particulate material ispressurized (for example, to a pressure of about 500 bar) and thenpassed to a zone of lower pressure. The rate at which the mixture ispassed to the low pressure zone is sufficiently high and the pressure ofthe low pressure zone is sufficiently low as to cause microfibrillationof the cellulose fibres. For example, the pressure drop may be effectedby forcing the mixture through an annular opening that has a narrowentrance orifice with a much larger exit orifice. The drastic decreasein pressure as the mixture accelerates into a larger volume (i.e., alower pressure zone) induces cavitation which causes microfibrillation.In an embodiment, microfibrillation of the fibrous substrate comprisingcellulose may be effected in a homogenizer under wet conditions,optionally in the presence of the inorganic particulate material. In thehomogenizer, the cellulose pulp and optional inorganic particulatematerial is pressurized (for example, to a pressure of about 500 bar),and forced through a small nozzle or orifice. The mixture may bepressurized to a pressure of from about 100 to about 1000 bar, forexample to a pressure of equal to or greater than 300 bar, or equal toor greater than about 500, or equal to or greater than about 200 bar, orequal to or greater than about 700 bar. The homogenization subjects thefibres to high shear forces such that as the pressurized cellulose pulpexits the nozzle or orifice, cavitation causes microfibrillation of thecellulose fibres in the pulp. Additional water may be added to improveflowability of the suspension through the homogenizer. The resultingaqueous suspension comprising microfibrillated cellulose and optionalinorganic particulate material may be fed back into the inlet of thehomogenizer for multiple passes through the homogenizer. When present,and when the inorganic particulate material is a naturally platymineral, such as kaolin, homogenization not only facilitatesmicrofibrillation of the cellulose pulp, but may also facilitatedelamination of the platy particulate material.

An exemplary homogenizer is a Manton Gaulin (APV) homogenizer.

After the microfibrillation step has been carried out, the aqueoussuspension comprising microfibrillated cellulose and optional inorganicparticulate material may be screened to remove fibre above a certainsize and to remove any grinding medium.

For example, the suspension can be subjected to screening using a sievehaving a selected nominal aperture size in order to remove fibres whichdo not pass through the sieve. Nominal aperture size means the nominalcentral separation of opposite sides of a square aperture or the nominaldiameter of a round aperture. The sieve may be a BSS sieve (inaccordance with BS 1796) having a nominal aperture size of 150 μm, forexample, a nominal aperture size 125 μm, or 106 μm, or 90 μm, or 74 μm,or 63 μm, or 53 μm, 45 μm, or 38 μm. In one embodiment, the aqueoussuspension is screened using a BSS sieve having a nominal aperture of125 μm. The aqueous suspension may then be optionally dewatered.

It will be understood therefore that amount (i.e., % by weight) ofmicrofibrillated cellulose in the aqueous suspension after grinding orhomogenizing may be less than the amount of dry fibre in the pulp if theground or homogenized suspension is treated to remove fibres above aselected size. Thus, the relative amounts of pulp and optional inorganicparticulate material fed to the grinder or homogenizer can be adjusteddepending on the amount of microfibrillated cellulose that is requiredin the aqueous suspension after fibres above a selected size areremoved.

In certain embodiments, the microfibrillated cellulose may be preparedby a method comprising a step of microfibrillating the fibrous substratecomprising cellulose in an aqueous environment by grinding in thepresence of a grinding medium (as described herein), wherein thegrinding is carried out in the absence of inorganic particulatematerial. In certain embodiments, inorganic particulate material may beadded after grinding to produce the top ply slurry, or ply slurry.

In certain embodiments, the grinding medium is removed after grinding.

In other embodiments, the grinding medium is retained after grinding andmay serve as the inorganic particulate material, or at least a portionthereof. In certain embodiments, additional inorganic particulate and/oradditive other than inorganic particulate material may be added aftergrinding.

The following procedure may be used to characterise the particle sizedistributions of mixtures of inorganic particulate material (e.g., GCCor kaolin) and microfibrillated cellulose pulp fibres.

Calcium Carbonate

A sample of co-ground slurry sufficient to give 3 g dry material isweighed into a beaker, diluted to 60 g with deionised water, and mixedwith 5 cm³ of a solution of sodium polyacrylate of 1.5 w/v % active.Further deionised water is added with stirring to a final slurry weightof 80 g.

Kaolin

A sample of co-ground slurry sufficient to give 5 g dry material isweighed into a beaker, diluted to 60 g with deionised water, and mixedwith 5 cm³ of a solution of 1.0 wt % sodium carbonate and 0.5 wt %sodium hexametaphosphate. Further deionised water is added with stirringto a final slurry weight of 80 g.

The slurry is then added in 1 cm³ aliquots to water in the samplepreparation unit attached to the Mastersizer S until the optimum levelof obscuration is displayed (normally 10-15%). The light scatteringanalysis procedure is then carried out. The instrument range selectedwas 300RF: 0.05-900, and the beam length set to 2.4 mm.

For co-ground samples containing calcium carbonate and fibre therefractive index for calcium carbonate (1.596) is used. For co-groundsamples of kaolin and fibre the RI for kaolin (1.5295) is used.

The particle size distribution is calculated from Mie theory and givesthe output as a differential volume based distribution. The presence oftwo distinct peaks is interpreted as arising from the mineral (finerpeak) and fibre (coarser peak).

The finer mineral peak is fitted to the measured data points andsubtracted mathematically from the distribution to leave the fibre peak,which is converted to a cumulative distribution. Similarly, the fibrepeak is subtracted mathematically from the original distribution toleave the mineral peak, which is also converted to a cumulativedistribution. Both these cumulative curves may then be used to calculatethe mean particle size (d₅₀) and the steepness of the distribution(d₃₀/d₇₀×100). The differential curve may be used to find the modalparticle size for both the mineral and fibre fractions.

EXAMPLES Example 1

A number of aqueous compositions comprising microfibrillated celluloseand inorganic particulate material were prepared by co-grinding Botniapulp in the presence of the inorganic particulate materials, asdescribed in detail elsewhere in this specification. Properties of eachcomposition are summarized in Table 1. POP refers to the “percentage ofpulp” wherein the POP is the percentage of the dry weight of the samplethat is pulp or fibrils rather than inorganic particulate material.

TABLE 1 Brookfield Total solids Tensile index Viscosity Composition (wt%) POP (wt %) (nm/g) (mPas) 50 POP 2.5 47.4 8.5 1280 Botnia/CalciumCarbonate 50 POP 2.2 49.5 7.1 2780 Botnia/Kaolin 20 POP 4.9 21.8 8.03540 Botnia/Kaolin 50 POP 1.9 51.0 9.4 1600 Botnia/Talc

Example 2

An additive was added to each slurry and mixed for 1 minute. The mixturewas allowed to stand for 60 minutes and then was filtered. The resultantfilter cake was placed in a laboratory oven at 80° C. until dry (<1 wt.% moisture).

The dried composition was then re-dispersed on a laboratory Silversonmixer. (Diluted to 20 POP, 1 minute Silverson mixing)

Each of compositions 1 through 4 was additized with different aditives(sodium chloride, glycol, urea, carboxynmethyl cellulose, sugar and guargum) at varying concentrations and tensile index determined. Averagedresults are summarized in Table 2.

TABLE 2 Reduction in tensile Reduction in tensile index upon drying withComposition index upon drying (%) additive (%) 50 POP Calcium 53 25Carbonate/Botnia 50 POP Kaolin/Botnia 25 0 20 POP Kaolin/Botnia 34 28 50POP Talc/Botnia 37 32

Example 3

The purpose of these trials was to evaluate the effectiveness ofre-dispersing a 50 wt. % POP (percentage of pulp) calciumcarbonate/Botnia pulp high solids microfibrillated cellulose and calciumcaerbonate composition (i.e., a 1:1 wt. ratio of microfibriallatedcellulose to calcium carbonate) using a single disc refiner available ata pilot plant facility. An example of a single disc refiner suitable foruse in the present invention was manufactured by Sprout Waldron. Therefiner was a 12 in (30 cm) single disc refiner. Disc rotational speedwas 1320 rpm. Disc peripheral velocity was 21.07 m/s. Refiner DiscDesign Bar width 1.5 mm; groove width 1.5 mm; bar cutting edge length1.111 Km/rev bar CEL @ 1320 rpm 24.44 Km/sec. Other suitable refinerswith equivalent specifications are known to those of ordinary skill inthe art.

Feed Materials.

Transported to the pilot plant facility was 100 kg of belt press cake ofmicrofibrillated cellulose and calcium carbonate (1:1 weight ratio) and100 kg of four different feed materials made utilizing an Atritordryer-pulverizer (available from Atritor Limited, 12 The Stampings, BlueRibbon Park, Coventry, West Midlands, England), which is an air-sweptmill or dryer having the capability to introduce a stream of hot air fordrying and milling materials, in order to process and dry themicrofibrillated cellulose and calcium carbonate composition utilized inthe trials. Other equivalent mills are known to one of ordinary skill inthe art. The properties of the calcium carbonate (IC60L)/Botnia highsolids microfibrillated cellulose products utilized in the trials areshown in Table 3. These microfibrillated cellulose and calcium carbonatecompositions (1:1 wt. ratio) were produced using an Atritor dryer withthe rejector arms in place and fed at 20 Hz (slow feed rate).

TABLE 3 Properties of the feed materials used for the single discrefined trial. Total solids FLT Index* Viscosity Feed Bag wt. % POP wt.% Nm/g gsm mPas 50 POP IC60/Botnia Beltpress cake 30.8 49.2 8.5 223 1440Atritor product bag 6 50 POP IC60/Botnia 51.4 50.6 8.1 226 1340 Atritorproduct bag 3 50 POP IC60/Botnia 58.1 47.6 7.1 223 940 Atritor productbag 2 50 POP IC60/Botnia 69.5 47.3 4.9 225 640 Atritor product bag 1 50POP IC60/Botnia 87.5 46.7 3.6 221 480 *After 1 minute of re-dispersion(between 1000-2000 kWh/t) using a laboratory scale Silverson mixer.

Trial Outline

Each material was “wetted” in a large pulper to replicate typicaltimes/actions in a paper mill operation.

The pulped samples passed through the single disc refiner with samplestaken at refining energy inputs ranging between 0-20-40-60-80-100 kWh/tof total dry solids.

Results.

1. 50 wt. % POP Calcium Carbonate (IC60)/Botnia Pulp (31 wt. % Solids)Belt Press Cake

This 30.5 wt. % solids belt pressed cake of a composition comprisingmicrofibrillated cellulose and calcium carbonate (1:1 wt. ratio) wasinitially re-dispersed in the pulper for 15 minutes at 7 wt. % solids.This consistency was too viscous to pump so the material was dilutedwith water by 1 wt. % to 6 wt. % solids. This material was then passedthrough the refiner and samples were taken at various work inputs.

Table 4 below shows the effect of the single disc refiner on theproperties of the belt pressed cake comprising microfibrillatedcellulose and calcium carbonate. The values quoted for the as receivedmaterial have been subjected to 1 minute of mixing in a Silverson mixer(Silverson Machines, Inc., 55 Chestnut St. East Longmeadow, Mass. 01028)which equates to 1000-2000 kWh/t.

TABLE 4 Properties of the single disc refined belt pressed cake Feed Bagtotal Refiner Energy Total FLT Index Viscosity Total Nib Surface AreaFeed Bag solids wt. % solids wt. % kWh/T solids POP wt. % Nm/g gsm mPasper gram mm²/g 50 POP IC60 30.5 7 as rec'd 30.8 49.2 [8.5] [223] [1440][0] Beltpress cake 0 6.4 49.0 5.5 222  980 5 50 POP IC60/Botnia 30.5 6as rec'd 30.8 49.2 [8.5] [223] [1440] [0] Beltpress cake 0 5.3 49.0 6.7227 1220 2 20 5.9 49.0 9.7 227 1960 1 40 5.7 49.1 8.5 220 1460 1 60 5.949.0 10.4 228 1940 1 80 6.0 49.2 10.6 231 1840 1 100 6.0 49.2 11.3 2241860 0

It can be seen that the belt press cake can be refined at 6 wt. % solidsand after an input of 20 kWh/t the FLT Index has been restored. The FLTindex is a tensile test developed to assess the quality ofmicrofibrillated cellulose and re-dispersed microfibrillated cellulose.The POP of the test material is adjusted to 20% by adding whicheverinorganic particulate was used in the production of the microfibrillatedcellulose/inorganic material composite (in the case of inorganicparticulate free microfibrillated cellulose then 60 wt. %<2 um GCCcalcium carbonate is used). A 220 gsm (g/m²) sheet is formed from thismaterial using a bespoke Buchner filtration apparatus The resultantsheet is conditioned and its tensile strength measured using an industrystandard tensile tester. Energy inputs up to 100 kWh/t can improve boththe FLT Index and viscosity of the microfibrillated cellulose andcalcium carbonate composition. The “nib count” of 1 and below isacceptable and suggests good formation of a paper sheet. As is known toone of ordinary skill in the art, the nib count is a dirt count test(see for example the TAPPI dirt count test) and is an indication thatthe microfibrillated cellulose has been fully redispersed. In this casethe sheets formed to measure the FLT index are subjected to nib countingusing a light box prior to the destructive tensile testing. A low nibcount is indicative of good redispersion in any aqueous application.

Table 5 shows the effect the single disc refiner has had upon theparticle size of the microfibrillated cellulose and calcium carbonatecomposition. The particle size distribution (“PSD”) has been measured ona Malvern Insitec (Malvern Instruments Ltd, Enigma Business Park,Grovewood Road, Malvern, WR14 1XZ, United Kingdom) located at thequality control laboratory facility.

TABLE 5 PSD properties of the single disc refined pressed cake RefinerTotal solids Energy solids Malvern Insitec Fractionation Trial ID wt. %kWh/T wt. % D10 D30 D50 D70 D90 −25 um +25-150 um +150-300 um +300 um 50POP IC60 7 as rec'd 30.8 11.7 44.4 102.6 210.5 508.2 20.3 40.3 18.4 21.0Beltpress cake 0 6.4 13.8 53.9 119.4 228.7 492.6 17.5 39.3 21.2 22.0 50POP IC60/Botnia 6 as rec'd 30.8 11.7 44.4 102.6 210.5 508.2 20.3 40.318.4 21.0 Beltpress cake 0 5.3 13.4 51.6 114.9 223.9 508.5 18.1 39.920.2 21.9 20 5.9 11.6 38.9 86.3 170.4 399.9 21.6 44.8 18.0 15.8 40 5.710.1 34.5 78.5 152.9 342.0 23.8 45.7 17.9 12.6 60 5.9 10.1 31.5 68.8131.5 286.0 25.0 48.9 16.9 9.2 80 6.0 9.9 30.8 67.6 128.9 280.2 25.549.1 16.6 8.9 100 6.0 9.7 29.1 62.4 118.0 252.8 26.5 50.7 15.7 7.1

It can be seen from the PSD values that the single disc refiner is veryefficient in reducing the coarse particles of the microfibrillatedcellulose and calcium carbonate composition.

2. 50 wt. % POP Calcium Carbonate (IC60)/Botnia Pulp MicrofribrillatedCellulose and Calcium Carbonate (1:1 wt. Ratio) Dried in an AtritorDryer (51.4 wt. % Solids).

This 51.4 wt. % 1:1 wt. ratio of microfibrillated cellulose and calciumcarbonate product dried utilizing an Atritor dryer was re-dispersedwithin the pulper at 7 wt. % solids. This material's low viscosityenabled it to pump easily. This material was then passed through therefiner and samples were taken at various work inputs.

Table 6 below shows the effect of the single disc refiner on theproperties of the 51.4 wt. % microfibrillated cellulose and calciumcarbonate composition. The values quoted for the as rec'd material havebeen subjected to 1 minute of mixing with a Silverson mixer whichequates to 1000-2000 kWh/t.

TABLE 6 Properties of the single disc refmined 51.4 wt. % compositioncomprising microfibrillated cellulose and calcium carbonate (1:1 wt.ratio) dried in an Atritior dryer. Feed Bag Refiner Energy Total FLTIndex Viscosity Total Nib Feed Bag total solids kWh/T solids POP wt. %Nm/g gsm mPas Surface Atritor product bag 50.8 7 as rec'd 51.4 50.6[8.1] [226] [1340] [2] 6 50 POP 0 6.9 50.5 5.6 198  660 — IC60/Botnia 206.5 49.7 8.0 234 1480 3 40 6.5 49.9 9.3 228 1540 2 60 6.7 49.9 9.9 2201480 1 80 6.3 49.9 11.3 228 1680 0 100 6.9 50.2 10.7 218 1420 0

This 51.4 wt. % dried composition dried in the Atritor dryer can betotally re-dispersed using 60 kWh/t and the properties improve evenfurther with increased energy input. This material regains viscosity andFLT Index as well as having a relatively low nib count similar to thebelt pressed cake.

Table 7 shows the effect the single disc refiner has had upon theparticle size of the composition comprising microfibrillated celluloseand calcium carbonate (1:1 wt. ratio).

TABLE 7 PSD properties of the single disc refined 51.4 wt. % compositioncomprising microfibrillated cellulose and calcium carbonate (1:1 wt.ratio) dried in the Atritor dryer. Refiner Total solids Energy solidsMalvern Insitec Fractionation Trial ID wt. % kWh/T wt. % D10 D30 D50 D70D90 −25 um +25-150 um +150-300 um +300 um Atritor product bag 7 as rec'd51.4 10.0 37.9 90.1 184.3 416.6 22.8 41.5 18.6 17.2 6 50 POP 0 6.9 8.632.2 80.4 165.5 368.4 25.4 41.8 18.2 14.6 IC60/Botnia 20 6.5 10.6 35.683.0 170.6 397.3 23.2 43.3 17.7 15.9 40 6.5 10.1 32.1 72.7 144.6 329.224.7 46.3 17.1 11.9 60 6.7 9.1 28.3 62.8 122.6 271.9 27.2 48.5 16.0 8.380 6.3 9.0 26.7 57.4 110.3 242.1 28.4 50.6 14.6 6.5 100 6.9 8.3 24.250.7 97.8 214.3 30.8 51.2 13.1 4.8

It can be seen from the PSD values that the single disc refiner is veryefficient in reducing the coarse particles of the microfibrillatedcellulose and calcium carbonate 1:1 wt. ratio composition.

3. 50 wt. % POP Calcium Carbonate (IC60)/Botnia Pulp MicrofibrillatedCellulose and Calcium Carbonate 1:1 wt. Ratio Composition Dried in anAtritor Dryer (58.1 wt. % Solids).

This 58.1 wt. % solids composition comprising microfibrillated celluloseand calcium carbonate (1:1 wt. ratio) was evaluated at 7, 8 and 9 wt %solids. The reason for this was that the higher energy inputs could notbe achieved because the composition comprising microfibrillatedcellulose and calcium carbonate became too “thin” in consistency and themetal disc of the refiner was rubbing on itself. Table 9 below shows theproperties of all the products at the three different solids contents.The values quoted for the as rec′d material and 0 kWh/t have beensubjected to 1 minute of mixing in a Silverson mixer, which equates to1000-2000 kWh/t.

TABLE 9 Properties of the single disc refined 58.1 wt. % Atritor productFeed Bag Refiner Energy Total FLT Index Viscosity Total Nib Feed Bagtotal solids kWh/T solids POP wt. % Nm/g gsm mPas Surface Atritorproduct bag 57.9 7 as rec'd 58.1 47.6 [7.1] [223] [940] [2] 3 50 POP 06.0 47.1 [5.9] [209] [640] — IC60/Botnia 20 6.4 47.0 3.9 223 540 — 407.1 46.9 6.7 224 940 — 60 6.8 47.0 8.4 225 1140  2 57.9 8 0 7.7 47.0[5.8] [199] [560] — 20 7.9 46.9 4.7 223 640 — 40 8.0 46.9 7.3 224 960 —60 7.8 47.1 8.8 222 1120  1 80 8.6 47.0 9.1 214 1040  1 57.9 9 0 8.047.2 [6.0] [211] [680] — 20 7.1 47.0 4.7 216 640 — 40 7.8 47.0 8.4 2251080  2 60 8.4 47.2 8.6 220 1120  1 80 8.5 47.0 9.6 222 1160  1 100 9.147.0 9.9 215 1160  1

The 58.1 wt. % composition comprising microfibrillated cellulose andcalcium carbonate (1:1 wt. ratio) can be totally re-dispersed at 7, 8and 9 wt. % solids. At each consistency the control FLT has beenexceeded as well as the viscosity and nib count. At 9 wt. % solids thegreatest enhancement is achieved.

Table 10 shows the effect the single disc refiner has had upon theparticle size of the composition comprising microfibrillated celluloseand calcium carbonate (1:1 wt. ratio) at all three solids contentlevels.

Once again the PSD data show the efficiency of the single disc refineron altering size of the coarse pulp at all three consistencies.

TABLE 10 PSD properties of the Single Disc Refined 58.1 wt. % ofmicrofibrillated cellulose (1:1 wt. ratio) composition dried in anAtritor dryer. Refiner Total solids Energy solids Malvern InsitecFractionation Trial ID wt. % kWh/T wt. % D10 D30 D50 D70 D90 −25 um+25-150 um +150-300 um +300 um Atritor product bag 7 as rec'd 58.1 9.932.4 77.2 155.3 341.6 24.8 44.2 18.3 12.7 3 50 POP 0 6.0 9.2 28.1 67.1137.5 302.0 27.4 45.1 17.4 10.1 IC60/Botnia 20 6.4 9.7 31.3 76.6 166.5397.9 25.4 41.8 17.1 15.7 40 7.1 9.1 26.7 59.8 121.9 275.6 28.4 47.315.7 8.6 60 6.8 8.5 24.5 52.3 103.3 224.1 30.5 50.1 14.0 5.4 8 0 7.7 9.229.6 71.4 146.1 322.6 26.5 44.2 17.7 12.1 20 7.9 9.4 28.7 67.6 146.3363.7 26.9 43.7 15.8 13.6 40 8.0 8.5 24.3 52.1 104.3 232.5 30.7 49.314.1 6.0 60 7.8 8.1 23.1 48.4 95.4 206.0 32.1 50.7 12.8 4.4 80 8.6 7.521.3 42.9 83.6 176.7 34.7 51.7 10.7 2.8 9 0 8.0 9.4 29.9 72.6 148.5332.0 26.3 44.0 17.7 12.1 20 7.1 9.4 29.2 69.5 147.5 351.1 26.7 43.816.6 12.9 40 7.8 8.9 24.8 52.6 105.2 233.7 30.2 49.6 14.1 6.1 60 8.4 7.922.5 46.8 90.7 190.5 32.9 51.7 11.9 3.5 80 8.5 7.4 20.9 42.0 81.7 168.435.3 52.1 10.1 2.5 100 9.1 6.9 19.6 38.5 74.6 153.9 37.4 52.1 8.8 1.8

4. 50 wt. % POP Calcium Carbonate (IC60)/Botnia Pulp MicrofibrillatedCellulose and Calcium Carbonate Composition Dried in an Atritor Dryer(70.1 wt. % Solids).

This 70.1 wt. % solids microfibrillated cellulose and calcium carbonate(1:1 wt. ratio) composition at each work input are shown in Table 11.The values quoted for the as rec′d material and 0 kWh/t have beensubjected to 1 minute of mixing in a Silverson mixer, which equates to1000-2000 kWh/t.

TABLE 11 Properties of the single disc refined 70.1 wt. %microfibrillated cellulose and calcium carbonate (1:1 wt. ratio)composition dried in an Atritor dryer. Feed Bag Refiner Energy Total FLTIndex Viscosity Total Nib Feed Bag total solids kWh/T solids POP wt. %Nm/g gsm mPas Surface Atritor product bag 70.1 9 as rec'd 69.5 47.3[4.9] [225] [640] [2] 2 50 POP 0 7.6 47.2 [3.5] [193] [340] —IC60/Botnia 20 7.6 46.9 2.7 219 400 — 40 9.1 46.9 5.1 218 620 — 60 10.047.1 6.7 216 720 — 80 9.7 47.1 7.3 219 760 1 100 9.5 47.0 8.4 218 920 0

Once again it can be seen that the single disc refiner is much moreefficient in re-dispersing the dried composition comprisingmicrofibrillated cellulose and calcium carbonate (1:1 wt. ratio)compared to using a Silverson mixer. An energy input of 100 kWh/tre-disperses the composition comprising microfibrillated cellulose andcalcium carbonate (1:1 wt. ratio) to a degree where the properties aresimilar to the belt pressed cake.

Table 12 shows the effect the single disc refiner has had upon theparticle size of the composition comprising microfibrillated celluloseand calcium carbonate (1:1 wt. ratio) and once again the refiner isshown to be very efficient.

TABLE 12 PSD properties of the single disc refined 70.1 wt. %composition comprising microfibrillated cellulose and calcium carbonate(1:1 wt. ratio) dried in an Atritor dryer. Refiner Total solids Energysolids Malvern Insitec Fractionation Trial ID wt. % kWh/T wt. % D10 D30D50 D70 D90 −25 um +25-150 um +150-300 um +300 um Atritor product bag 9as rec'd 69.5 10.8 38.9 96.7 200.0 436.5 22.3 39.6 19.4 18.8 2 50 POP 07.6 9.2 30.7 77.5 161.8 352.9 26.0 41.9 18.6 13.5 IC60/Botnia 20 7.610.4 35.5 89.0 193.6 451.3 23.5 39.8 17.8 18.9 40 9.1 8.7 26.0 58.5119.3 268.4 29.0 47.2 15.7 8.1 60 10.0 7.9 22.8 48.3 95.4 202.6 32.450.6 12.8 4.2 80 9.7 7.5 21.2 42.9 83.7 174.7 34.8 51.9 10.6 2.8 100 9.57.4 20.4 39.4 75.1 156.3 36.3 52.8 9.0 1.9

5. 50 wt. % POP Calcium Carbonate (IC60)/Botnia Pulp CompositionComprising Microfibrillated Cellulose and Calcium Carbonate (1:1 wt.Ratio) Dried in an Atritor Dryer (86.2 wt. % Solids).

This material at 86.2 wt. % solids composition comprisingmicrofibrillated cellulose and calcium carbonate (1:1 wt. ratio) wasdeemed to be very dry so the composition was refined under the sameconditions as the rest of the materials (intensity of 0.2 J/m) but alsoat an intensity of 0.1 J/m. 0.1 J/m is less intense so it takes longerto achieve the desired work input. See, Table 13.

The values quoted for the as received material and 0 kWh/t have beensubjected to 1 minute of mixing in a Silverson mixer, which equates to1000-2000 kWh/t.

TABLE 13 Properties of the single disc refined 86.2 wt. % compositioncomprising microfibrillated cellulose and calcium carbonate (1:1 wt.ratio) dried in an Atritor dryer. Feed Bag Refiner Energy Total FLTIndex Viscosity Total Nib Feed Bag total solids kWh/T solids POP wt. %Nm/g gsm mPas Surface Atritor product bag 86.2 9   as rec'd 87.5 46.7[3.6] [221] [480] [2] 1 50 POP Intensity 0 4.8 46.6 [4.2] [253] [740] —IC60/Botnia 0.2 20 7.3 46 2.3 217 320 — 40 9.5 47.4 4.2 220 500 — 60 9.446.1 5.7 218 640 — 80 9.8 46.1 7.0 219 740 1 100 9.4 46.2 7.9 221 880 1Atritor product bag 86.2 9   as rec'd 87.5 46.7 [3.6] [221] [480] [2] 150 POP Intensity 0 6.0 46.5 [2.2] [196] [240] — IC60/Botnia 0.1 20 8.745.9 4.3 219 480 — 40 9.7 46.1 6.4 215 680 — 60 9.3 45.9 7.9 225 940 080 10.2 45.9 8.4 215 840 0

These results show that this very high solids composition comprisingmicrofibrillated cellulose and calcium carbonate (1:1 wt. ratio) can bere-dispersed back to the same properties as the belt pressed cake using100 kWh/t. If the intensity is changed then the properties can berestored using less energy of 80 kWh/t.

Table 14 shows the effect the single disc refiner has had upon theparticle size of the composition comprising microfibrillated celluloseand calcium carbonate (1:1 wt. ratio) at both intensities.

TABLE 14 PSD properties of the single disc refined 86.2 wt. %composition comprising microfibrillated cellulose and calcium carbonate(1:1 wt. ratio) dried in an Atritor dryer. Refiner Total solids Energysolids Malvern Insitec Fractionation Trial ID wt. % kWh/T wt. % D10 D30D50 D70 D90 −25 um +25-150 um +150-300 um +300 um Atritor product bag9   as rec'd 87.5 10.2 37.4 97.7 212.0 450.9 23.1 37.6 19.0 20.3 1 50POP Intensity 0 4.8 11.2 37.3 95.4 206.1 442.5 22.7 38.8 19.0 19.6IC60/Botnia 0.2 20 7.3 9.6 34.0 88.5 197.0 468.4 24.4 38.5 17.7 19.4 409.5 8.3 24.9 56.5 117.1 266.7 30.1 46.6 15.4 8.0 60 9.4 7.8 22.1 46.192.0 198.3 33.5 50.2 12.4 4.0 80 9.8 7.3 20.5 41.2 81.1 176.8 35.9 50.810.1 3.3 100 9.4 6.9 19.2 36.7 70.4 145.5 38.3 52.2 7.9 1.6 Atritorproduct bag 9   as rec'd 87.5 10.2 37.4 97.7 212.0 450.9 23.1 37.6 19.020.3 1 50 POP Intensity 0 6.0 9.1 32.6 88.6 190.8 394.7 25.3 38.0 19.717.0 IC60/Botnia 0.1 20 8.7 8.6 26.9 63.4 132.1 298.8 28.3 45.2 16.6 9.940 9.7 7.6 21.7 45.1 90.1 195.7 34.0 50.1 11.8 4.1 60 9.3 7.1 20.2 40.780.3 167.8 36.2 51.3 9.8 2.7 80 10.2 6.5 18.6 35.5 69.1 142.2 39.4 51.67.6 1.4

FIG. 1. summarises the FLT data from the above studies. The data showthat the control FLT can be achieved in all the samples tested and thatthe control FLT can be exceeded in the intermediate solid products.

6. Further Processing of Refined Products

On a number of the products produced at pilot plant facility extraenergy was put into the samples via the Silverson mixer. Theseexperiments were to investigate whether the physical properties of thecomposition comprising microfibrillated cellulose and calcium carbonate(1:1 wt. ratio) would be improved with extra energy. The following tableshows the findings, (Table 15).

It can be seen that the results are mixed. On some occasions there is anincrease in FLT Index and on others there is not.

TABLE 15 The effect of extra energy input NO Silverson 0.5 minute 1minute 2 minutes 3 minutes Feed Bag total Refiner Energy Total FLT indexFLT Index FLT Index FLT index FLT Index Feed Bag solids wt. % solids wt.% kWh/T solids POP wt. % Nm/g Nm/g Nm/g Nm/g Nm/g 50 POP IC60 30.5 7 asrec'd 30.8 49.2 — 7.5 8.5 8.8 9.2 Beltpress cake 0 6.4 49.0 5.5 — 8.8 —— 50 POP IC60/Botnia 30.5 6 as rec'd 30.8 49.2 — 7.5 8.5 8.8 9.2Beltpress cake 0 5.3 49.0 — — 9.2 — — 20 5.9 49.0 9.7 10.2  11.2  — — 405.7 49.1 8.5 10.0  9.0 — — 60 5.9 49.0 10.4  10.6  11.1  — — 80 6.0 49.210.6  10.8  11.0  — — 100 6.0 49.2 11.3  11.4  11.1  11.0  11.3  Atritorproduct bag 6 50.8 7 as rec'd 51.4 50.6 — 7.2 8.1 8.5 9.0 50 POPIC60/Botnia 0 6.9 50.5 — — 5.6 — — 20 6.5 49.7 8.0 — — — — 40 6.5 49.99.3 — — — — 60 6.7 49.9 9.9 — — — — 80 6.3 49.9 11.3  — — 12.2  11.9 100 6.9 50.2 10.7  — — — — Atritor product bag 3 57.9 7 as rec'd 58.147.6 — 5.3 7.1 7.3 8.4 50 POP IC60/Botnia 0 6.0 47.1 — — 5.9 — — 20 6.447.0 3.9 — — — — 40 7.1 46.9 6.7 — — — — 60 6.8 47.0 8.4 — — — — 57.9 80 7.7 47.0 — — 5.8 — — 20 7.9 46.9 4.7 — — — — 40 8.0 46.9 7.3 — — — —60 7.8 47.1 8.8 — — — — 80 8.6 47.0 9.1 — — — — 57.9 9 0 8.0 47.2 — —6   — — 20 7.1 47.0 4.7 — — — — 40 7.8 47.0 8.4 — — — — 60 8.4 47.2 8.6— — — — 80 8.5 47.0 9.6 — — — — 100 9.1 47.0 9.9 — — — — Atritor productbag 2 70.1 9 as rec'd 69.5 47.3 — 3.3 4.9 5.9 6.6 50 POP IC60/Botnia 07.6 47.2 — — 3.5 — — 20 7.6 46.9 2.7 — — — — 40 9.1 46.9 5.1 — — — — 6010.0 47.1 6.7 — — — — 80 9.7 47.1 7.3 — — — — 100 9.5 47.0 8.4 8.2 8.48.7 8.7 Atritor product bag 1 86.2 9 as rec'd 87.5 46.7 — 2.2 3.6 4.65   50 POP IC60/Botnia Intensity 0 4.8 46.6 — — 4.2 — — 0.2 20 7.3 462.3 4.6 5.6 — — 40 9.5 47.4 4.2 5.5 6.3 — — 60 9.4 46.1 5.7 6.9 7.2 — —80 9.8 46.1 7.0 7.7 8.3 — — 100 9.4 46.2 7.9 8.7 9   — — Atritor productbag 1 86.2 9 as rec'd 87.5 46.7 — 2.2 3.6 50 POP IC60/Botnia Intensity 06.0 46.5 — — 2.2 — — 0.1 20 8.7 45.9 4.3 5.8 6.3 — — 40 9.7 46.1 6.4 7.07.4 — — 60 9.3 45.9 7.9 9.0 8.9 — — 80 10.2 45.9 8.4 8.7 8.8 8.4 8.2

Results.

The results show:

-   -   The single disc refiner at pilot plant facility is a very        efficient way of re-dispersing a composition comprising        microfibrillated cellulose and calcium carbonate (1:1 wt. ratio)    -   A composition comprising microfibrillated cellulose and calcium        carbonate (1:1 wt. ratio) dried up to 86 wt. % solids can be        re-dispersed to achieve its original strength characteristics.    -   An enhancement on strength can be achieved.    -   The single disc refiner achieves re-dispersion using low energy        inputs than other evaluated methods.    -   The solids content is very important when refining and should be        optimised for all samples.    -   Lowering the intensity of the refiner achieves improved results.    -   The single disc refiner is very efficient in altering the PSD of        a composition comprising microfibrillated cellulose and calcium        carbonate (1:1 wt. ratio).

1. A method of improving the physical and/or mechanical properties ofre-dispersed dried or partially dried microfibrillated cellulose, themethod comprising: a. providing: an aqueous composition ofmicrofibrillated cellulose; b. dewatering the aqueous composition by oneor more of: i. dewatering by belt press, ii. a high pressure automatedbelt press, iii. centrifuge, iv. tube press, v. screw press, and vi.rotary press; to produce a dewatered microfibrillated cellulosecomposition; c. drying the dewatered microfibrillated cellulosecomposition by one or more of: i. a fluidized bed dryer, ii. microwaveand/or radio frequency dryer, iii. a hot air swept mill or dryer, a cellmill or a multirotor cell mill, and iv. freeze drying; to produce adried or partially dried microfibrillated cellulose composition;whereupon re-dispering the dried or partially dried microfibrillatedcellulose composition into a liquid medium, the microfibrillatedcellulose has a tensile index and/or viscosity which is at least 50% ofthe tensile index and/or viscosity of the aqueous composition ofmicrofibrillated cellulose prior to drying at a comparable concentrationand a fibre steepness of from 20 to
 50. 2. A method according to claim1, further comprising re-dispersing the dried or at least partiallydried microfibrillated cellulose in the liquid medium.
 3. The method ofclaim 1, wherein said microfibrillated cellulose additionally comprisesan inorganic particulate material.
 4. The method of claim 3, wherein theinorganic particulate material comprises a platy mineral, kaolin and/ortalc.
 5. The method of claim 4, wherein the inorganic particulatematerial additionally comprises inorganic particulate material otherthan a platy mineral.
 6. The method of claim 3, wherein the inorganicparticulate material is calcium carbonate.
 7. The method of claim 1,wherein said dried or partially dried microfibrillated cellulose isre-dispersed in the presence of one or more additives selected from thegroup consisting of one or more salts, one or more sugars, one or moreglycols, urea, carboxymethyl cellulose and guar gum.
 8. A method ofclaim 5, wherein the sugar is selected from one or more ofmonosaccharides, disaccharides, oligosaccharides and polysachharides. 9.A method of claim 5, wherein the one or more salts comprise or is sodiumchloride.
 10. A method of claim 5, wherein the one or more glycolscomprise or is ethylene glycol.
 11. A method of claim 3, the whereininorganic particulate material is added at one or more of the followingstages: (i) prior to or during manufacture of the aqueous compositioncomprising microfibrillated cellulose; (ii) following manufacture of theaqueous composition comprising microfibrillated cellulose; (iii) duringdewatering of the aqueous composition of microfibrillated cellulose;(iv) during drying of the aqueous composition of microfibrillatedcellulose; (v) prior to re-dispersing of the dried or at least partiallydried microfibrillated cellulose; and (vi) during re-dispersing of thedried or at least partially dried microfibrillated cellulose.
 12. Themethod of claim 1, said method further comprising using the re-dispersedmicrofibrillated cellulose in, or in the manufacture of, an article,product or composition.
 13. The method of claim 1, wherein the aqueouscomposition of the dewatered microfibrillated cellulose prior to dryingor at least partially drying has a solids content of up to about 50 wt.%, up to about 30% and up to about 20%.
 14. The method of claim 3,wherein the aqueous composition of the dewatered microfibrillatedcellulose prior to drying or at least partially drying has a solidscontent of up to about 20 wt. %, optionally wherein up to about 80% ofthe solids is inorganic particulate material.
 15. The method of claim 2,wherein the liquid medium is aqueous or non-aqueous.
 16. The method ofclaim 15, wherein the liquid medium is aqueous, for example, water. 17.The method of claim 2, wherein said re-dispersing of the dried or atleast partially dried microfibrillated cellulose comprises using arefiner.
 18. The method of claim 1, wherein said a dried or partiallydried microfibrillated cellulose composition has a steepness from about20 to about 50.